Selina Class 8 ICSE Solutions

Selina Concise Chemistry Class 8 ICSE Solutions – Hydrogen

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Selina Concise Chemistry Class 8 ICSE Solutions – Hydrogen

ICSE SolutionsSelina ICSE SolutionsML Aggarwal Solutions

APlusTopper.com provides step by step solutions for Selina Concise ICSE Solutions for Class 8 Chemistry Chapter 7 Hydrogen. You can download the Selina Concise Chemistry ICSE Solutions for Class 8 with Free PDF download option. Selina Publishers Concise Chemistry for Class 8 ICSE Solutions all questions are solved and explained by expert teachers as per ICSE board guidelines.

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Selina Concise ICSE Solutions for Class 8 Chemistry Chapter 7 Hydrogen

Points to Remember:

  1. Hydrogen is the most abundant element found in the universe.
  2. Hydrogen is much more common in the form of compounds. The most important compound of hydrogen is water.
  3. The chief sources of hydrogen are water, acids and alkalies.
  4. Hydrogen is prepared by the action of water, acids or alkalies on active metals.
  5. Electrolysis of water results in the formation of hydrogen and oxygen.
  6. Hydrogen is lighter than air.
  7. Hydrogen bums in air with pop sound.
  8. Hydrogen acts as a reducing agent.
  9. Hydrogen is used to produce oxyhydrogen flame and in weather forecast balloons.

Exercise

1. Fill in the blanks:

(a) Hydrogen is lighter than air.
(b) Hydrogen is sparingly soluble in water.
(c) Hydrogen bums with a oxyhydrogen pale blue flame and pop sound is heard.
(d) A metal sodium hydrogen in the reactivity series gives hydrogen with water.
(e) Hydrogen reacts with metal oxides to form metal and water.
(f) Oxidation is the removal of hydrogen and addition of oxygen.
(g) In redox reaction oxidation and reduction occur simultaneously.

2. Indicate which of the following statements are true and which are false:

(a) Hydrogen molecule is monovalent.
(b) The removal of hydrogen from a substance is called reduction.
(c) Nitric acid can not be used to prepare hydrogen by its action on active metals ?
(d) The reaction between hydrogen and nitrogen to form ammonia is reversible.
(e) Zinc can liberate hydrogen from water, acid and alkali solution.
(f) Hydrogen is combustible as well as a supporter of combustion.
(g) Hydrogen gas is easily liquefiable.
Answer:
(a) False
(b) True
(c) False. Hydrogen cannot be prepared by the action of nitric acid on metals because it also releases nitrous oxide and nitric oxide.
(d) True
(e) True
(f) False
(g) False

3. Complete and balance the following equations:

selina-concise-chemistry-class-8-icse-solutions-hydrogen-1
selina-concise-chemistry-class-8-icse-solutions-hydrogen-2

4. Give reasons for the following:

(a) Hydrogen be used as a fuel?
(b) Though hydrogen is lighter than air it cannot be collected by downward displacement of air.
(c) A pop sound produced when hydrogen is burnt?
(d) Helium replaced hydrogen in weather observation balloons?
(e) Nitric acid not used for the preparation of hydrogen gas?
(a) Because of its high heat of combustion, it is used as a fuel.
Answer:
(a) Coal gas, water gas and liquid hydrogen are some significant fuel.
(b) Since hydrogen is lighter than air. it is possible to collect the gas by downward displacement of air. But it is not safe to do so since a mixture of hydrogen and air can lead to an explosion.
(c) Impure hydrogen gas bums in air with a pop sound. This is because of the presence of impurities in it.
(d) If there is small leakage of hydrogen in a balloon, it forms a mixture with air that can explode. So helium has replaced hydrogen.
(e) Hydrogen cannot be prepared by the action of nitric acid on metals because it also releases nitrous oxide and nitric oxide and oxides the hydrogen to form water.

5. Name the following:
(a) Two metals which give hydrogen with cold water.
(b) A metal which liberates hydrogen only when steam is passed over red hot metal.
(c) The process in which oxygen is added or hydrogen is removed.
(d) A metallic oxide which can be reduced into metal by hydrogen.
Answer:
(a) Sodium (Na) and Potassium (K) give hydrogen with cold water.
(b) Iron
(c) Oxidation
(d) Copper oxide (CuO)

6. (a) Name the chemicals required to prepare hydrogen
gas in the laboratory.
(b) Give a balanced chemical equation for the reaction.
(c) Draw a neat and well-labelled diagram for the laboratory preparation ofhydrogen.
(d) How is hydrogen gas collected?
Answer:
(a) Granulated Zinc and dil. Hydrochloric acid.
(b) Zn + 2 HCl → ZnCl2 + H2 (g)
(c)
selina-concise-chemistry-class-8-icse-solutions-hydrogen-3
(d) Hydrogen gas is collected by the down-ward displacement of water.

7. How would you show that hydrogen:
(a) is a non-supporter of combustion?
(b) is lighter than air?
Answer:
(a) Hold a hydrogen gas filled jar with its mouth downwards.
Place a lighted candle inside the jar. The candle gets extinguished but the gas bums with a pop sound. This shows that hydrogen is non-supporter of combustion.
selina-concise-chemistry-class-8-icse-solutions-hydrogen-4

(b) Take a delivery tube and place one of its ends in a soap solution kept in a trough and the other one in a flat bottom jar as shown in the figure. The soap bubbles containing hydrogen rise upward the air. The rising soap bubbles prove that hydrogen is lighter than air.
selina-concise-chemistry-class-8-icse-solutions-hydrogen-5
Hydrogen-filled soap bubbles rising upward in the soap solution and into the air shows that hydrogen is lighter than air.

8. Hydrogen is a good reducing agent: What do you understand by the above statement? Explain with the help of copper oxide as an example.
Answer:
Hydrogen acts as a good reducing agent means, when hydrogen gas is passed over hot metallic oxides of copper, lead, iron, etc. it removes oxygen from them and thus reduces them to their corresponding metal.
Let us consider the following example, in each of which metallic oxide react with hydrogen. Metallic oxide act as oxidising agents and hydrogen acts as a reducing agents.
selina-concise-chemistry-class-8-icse-solutions-hydrogen-6

9. (a) Name a process by which hydrogen gas is manufactured.
(b) Give equations for the reactions.
(c) How is hydrogen separated from carbon dioxide and carbon monoxide?
Answer:
(a) Commercially, hydrogen is prepared by Bosch process.

(b) (i) Steam is passed over hot coke at 1000°C in a furnace called converters. As a result water gas is produced which is a mixture of carbon monoxide and hydrogen gases.
selina-concise-chemistry-class-8-icse-solutions-hydrogen-7
This reaction is endothermic in nature.
(ii) Water gas is mixed with excess of steam and passed over a catalyst ferric oxide (Fe2O3) and a promotor chromium trioxide (Cr2O3).
selina-concise-chemistry-class-8-icse-solutions-hydrogen-8
This reaction is exothermic in nature

(c) (i) The products are hydrogen, carbon dioxide and some
unreacted carbon monoxide. Hydrogen is separated from carbon dioxide by passing the mixture through water under pressure, in which carbon dioxide gets dissolved leaving behind hydrogen. Carbon dioxide can also be separated by passing it through caustic potash (KOH) solution.
2KOH + CO2 → K2CO3 + H2O
(ii) To separate carbon monoxide the gaseous mixture is passed through ammoniacal cuprous chloride in which carbon monoxide dissolves leaving behind hydrogen.
selina-concise-chemistry-class-8-icse-solutions-hydrogen-9
Thus hydrogen gas is obtained.

10. Match the statements in Column A with those in Column B.
selina-concise-chemistry-class-8-icse-solutions-hydrogen-10

11. State four uses of hydrogen:
Answer:

  1. Hydrogen with oxygen produce oxy-hydrogen flame which is used for cutting and welding.
  2. Hydrogen gas is used as a fuel.
  3. Hydrogen is used for hydrogenation of vegetable oil.
  4. Hydrogen gas is used extensively in the manufacture of ammonia gas, which is used to produce fertilizers.

12. Define:
(a) catalytic hydrogenation (b) oxidation
(c) reduction (d) redox reaction
Answer:
(a) Catalytic hydrogenation: catalytic hydrogenation is a process by which hydrogen gas is passed through vegetable oils in the presence of catalyst like Ni, Pt or Pd to convert them into solid vanaspati ghee.

(b) Oxidation: A reaction in which a substance combine with oxygen or in which hydrogen is removed is called oxidation reaction.
Example: H2S + Cl → 2HCl + S

(c) Reduction: Those reactions in which hydrogen combines with a substance or oxygen is removed from a substance, are known as reduction reactions.
selina-concise-chemistry-class-8-icse-solutions-hydrogen-11

(d) Redox reaction: Redox reactions are those in which reduction and oxidation both takes place simultaneously i.e. one substance is reduced while the other gets oxidised.

13. Multiple Choice Questions

(a) Equal volumes of hydrogen and chlorine are exposed to diffused sunlight to prepare

  1. hydrogen chloride
  2. water
  3. sodium hydroxide
  4. hydrochloric acid

(b) The metal which reacts with cold water to produce hydrogen is

  1. magnesium
  2. aluminium
  3. calcium
  4. iron

(c) In metal activity series the more reactive metals are at

  1. top
  2. bottom
  3. middle
  4. none

(d) Hydrogen is responsible for producing

  1. heat and light
  2. hydrogenated oil
  3. fertilizers
  4. all of the above

(e) Hydrogen is

  1. combustible
  2. non-combustible
  3. supporter of combustion
  4. neither supporter nor combustible

(f) Water gas is a mixture of

  1. carbon monoxide and oxygen
  2. carbon monoxide and hydrogen
  3. hydrogen and oxygen
  4. hydrogen and nitrogen.

Selina Concise Biology Class 8 ICSE Solutions – Diseases and First Aid

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Selina Concise Biology Class 8 ICSE Solutions – Diseases and First Aid

ICSE SolutionsSelina ICSE SolutionsML Aggarwal Solutions

APlusTopper.com provides step by step solutions for Selina Concise ICSE Solutions for Class 8 Biology Chapter 8 Diseases and First Aid. You can download the Selina Concise Biology ICSE Solutions for Class 8 with Free PDF download option. Selina Publishers Concise Biology for Class 8 ICSE Solutions all questions are solved and explained by expert teachers as per ICSE board guidelines.

Selina Class 8 Biology ICSE SolutionsChemistryPhysicsMathsGeographyHistory & Civics

Selina Concise ICSE Solutions for Class 8 Biology Chapter 9 Diseases and First Aid

REVIEW QUESTIONS

Multiple Choice questions:

1. Put a tick mark (✓) against the correct alternative in the following statements:

(a) A mosquito is a vector for

  1. Typhoid
  2. Cholera
  3. Malaria
  4. Jaundice

(b) Dengue is caused by a

  1. Protozoan
  2. Virus
  3. Worm
  4. Fungus

(c) The idea of vaccination was conceived by

  1. Charles Darwin
  2. Alexander Flemming
  3. Issac Newton
  4. Edward Jenner

(d) Which one of the following is not a psychotropic drug ?

  1. Morphine
  2. Cocaine
  3. Heroin
  4. Penicillin

(e) Which one of the following is a communicable disease ?

  1. Measles
  2. Cancer
  3. Heart stroke
  4. Allergy

(f) Cataract is a disease of: –

  1. Ears
  2. Nose
  3. Eyes
  4. Throat

(g) Infectious diseases can be prevented by:

  1. Medicines
  2. Proper food
  3. Immunisation
  4. Exercise

(h) Which one of the following is a genetic disease ?

  1. Scurvy
  2. Leukemia
  3. Goitre
  4. Haemophilia

(i) Which one of the following is a degenerative disease ?

  1. Thalassemia
  2. Beri-beri
  3. Cataract
  4. Diabetes

(j) Pellagra is one disease caused by the deficiency of:

  1. Vit. B3
  2. Vit. B1
  3. Vit. C
  4. Vit. D

(k) Hay fever and asthma are

  1. Deficiency diseases
  2. Genetic diseases
  3. Organic diseases
  4. Allergy diseases

(I) Which one of the following vitamin deficiency diseases can be cured by eating a diet which includes carrot, yellow fruits, vegetables, butter, milk, fish ?

  1. Beri-beri
  2. Dermatitis
  3. Night blindness
  4. Scurvy

Short Answer Questions:

Question 1(a).
What is a non-communicable disease ?
Answer:
The diseases which are caused due to improper functioning of the body organs e.g. diabetes, heart attack. They are not caused by germs and not transmitted from one to another.

Question 1(b).
What are communicable diseases ?
Answer:
Those disease which spread from one person to another by the entry of microorganisms are known as communicable diseases.

Question 1(c).
How can we control spreading of diseases by mosquitoes and houseflies ?
Answer:
We can control spreading of diseases by mosquitoes and houseflies by using repellants, throwing garbage in covered bins, avoiding stagnation of water and checking breeding of these insects.

Question 1(d).
Public hygiene is equally important as personal hygiene. Give reasons.
Answer:
Keeping oneself clean is personal hygiene. But public hygiene is equally important as dirty surrounding may lead to more of houseflies, mosquitoes and other insects which are major vectors of many communicable diseases. Clean surrounding also provides good mental health as it soothes our mind.

Question 1(e).
What is a deficiency disease ?
Answer:
These disease are caused by lack of nutrients, vitamins, minerals as a anaemia, goitre.

Question 1(f).
Biting nails should be strictly avoided. Give reason.
Answer:
Nail biting may cause many disease as the dirt has many bacteria causing diseases. Nails should be cut from time to time to save from diseases.

Question 1(g).
Regular exercise and proper rest is a must. Give reason.
Answer:
Regular exercise keeps our body strong and immune to many diseases, rest refreshes our body.

Question 1(h).
Children eating more of fast food tend to suffer from obesity (overweight). Comment.
Answer:
Fast food like pizza, burger, patty, oily foods etc. have much carbohydrates and fats. Children eating these become more and more fat and gain weight soon as they do not do much of physical work.

2. Name the following:

Question 2(a).
A viral disease caused due to unhealthy sexual contact
Answer:
AIDS.

Question 2(b).
A disease caused due to Plasmodium
Answer:
Malaria.

Question 2(c).
A disease caused by the bite of female Anopheles mosquito
Answer:
Malaria.

Question 2(d).
Two viral diseases caused by mosquito bites
Answer:
Dengu, Chikungunya.

Question 2(e).
Any droplet — borne disease.
Answer:
Amoebiasis, Cholera, Hepatitis A.

Question 2(f).
A viral disease caused by the bite of a dog
Answer:
Rabies/Hydrophobia

Question 2(g).
A disease due to choking of coronary artery
Answer:
Atheraosclerosis.

Question 2(h).
Two diseases caused due to deficiency of protein in the diet of a child.
Answer:
Kwashiorkor and marasmus.

3. Write short (2-3 sentences) notes on the following:
Disease, immunisation, pathogen, AIDS, vaccination, vector.

Answer:

Disease: Disease is a departure from normal health due to structural or functional disorder of the body. Disease may be due to deficiency of nutrients or malfunctioning of organs or 1 genetic disorders, improper metabolic activity, or allergies, or cancer and mental illness as diabetes, haemophilia, leukemia, schizophrenia.

Immunisation: It means, we make the body immune to certain diseases by introducing respective weakened germs into the body. Thus we develop resistance to the concerned disease this process is called immunisation. The germs or the material introduced into the body to make it resistant to the concerned disease is called vaccine. This produces antibodies in the body of the person and the person can be saved by these antibodies. The vaccine can be given by the injection or orally as polio drops, tap vaccine for typhoid, BCG vaccine for tuberculosis.

Pathogens: The germs that cause diseases to human beings and to other animals and plants are called pathogens. They spread the diseases from person to person or through the air or through the articles of the diseased persons. Pathogens may be different kinds of bacteria, viruses, fungi, protozoans or worms.

AID’S (Acquired Immune Deficiency Syndrome): It is a viral disease caused by the virus called HIV (Human immuno deficiency virus) This virus makes the defence mechanism of the human body very weak. The immune system in the body as W.B.C. becomes weak. Thus the person catches the infectious diseases very easily. This disease spreads through sexual contact as one of the partner may be carrier of the disease. It may spread through the blood transfusion and infected syringes, blades of the barbers, it may infect the developing baby through the blood by the mother. It is very deadly disease.

Vaccination: Vaccination is a method of making the body immune to a particular disease by injecting killed or weakened disease causing microbe into a body to stimulate the formation of antibodies and develop immunity to that disease causing microbe.

Vector: A vector is an organism that carries disease causing microbes (pathogens) from one host to another. They are the carriers of infection. Example: Mosquito, housefly, etc.

P.Q. Fill in the blanks by selecting suitable words given below:
(clotting, goitre, insuline, rickets, iron, proteins)

(a) Anaemia is caused due to the deficiency of iron.
(b) Deficiency of Vit. D causes rickets in children.
(c) Deficiency of iodine in the diet may cause goitre.
(d) Diabetes is caused due to undersecretion of insulin.
(e) Kwashiorkor is caused due to the deficiency of proteins.
(f) Haemophilia is a disease caused due to slow clotting of the blood.

P.Q. Find the odd one out:

(a) Typhoid, cholera, jaundice, tuberculosis, tetanus.
Jaundice is odd one
(b) Cold, AIDS, plague, malaria, measles.
Malaria is odd one.
(c) Scurvy, rickets, haemophilia, pellagra, night blindness.
Haemophilia is odd one.
(d) Proteins, carbohydrates, fats, minerals, cancer.
Cancer is odd one.

P.Q. Fill in the blank in the following table:
Selina Concise Biology Class 8 ICSE Solutions – Diseases and First Aid 1
Answer:
Selina Concise Biology Class 8 ICSE Solutions – Diseases and First Aid 2
Selina Concise Biology Class 8 ICSE Solutions – Diseases and First Aid 3

Long Answer Questions:

Question 1.
What is vaccination? Mention the four ways in which vaccine’s are prepared, giving the name of one disease for which each type of vaccine is used.
Answer:
For developing resistance in the body we introduce germs or germ substances in the body to develop resistance in the body against a particular disease. The material introduced into the body is called vaccine, this practice is called prophylaxis.
The germ or the germ substance is put into the body orally as polio drops or it is introduced by injection as TAB vaccine. Vaccine or vaccination was attached with small pox, but it is now used in a general sense.

Preparation:

  1. Killed germs are introduced into the body These act as vaccine for TAB, vaccine for typhoid, Salk’s vaccine for poliomyelitis. Rabies vaccine for dog bite.
  2. Living weakened germs: The living germs are treated in such a way that they become very weak and as such, they cannot cause the disease. They can induce antibody formation such as the vaccine for measles and the freezed dried BCG vaccine for tuberculosis.
  3. Living fully virulent germs: These virulent germs in small doses are introduced into the body as vaccine and these produce antibodies in the body and these do not allow the germs of particular type to cause that disease: In this vaccination the person is inoculated with cowpox virus. It is very similar to small pox virus.
  4. Toxoids: Toxoids are prepared from the extracts., of toxins secreted by bacteria. These toxins are poisons and these are made harmless by adding formalin into them. They retain their capacity and as a result when introduced into the body they produce antibodies into the body and do not allow the germs to grow in the body as vaccines for diphtheria and tetanus.

Question 2.
Burns can be superficial burns, deep burns or chemical burns. What emergency care you would suggest in each case.
Answer:
When one gets burnt up accidentaly one should not pull clothes from the burnt area and one should not cut the blisters. One should apply butter, vaseline or ointment.

  • Superficial burns: When there are superficial bums, put cold water on it and apply some oily substance, bumol, castor oil, vaseline, butter etc.
  • Deep burns: When there are deep bums do not put cold water on the burnt area. Seek the help of hospital and one should be kept under the treatment of some expert doctor of skin.
  • Chemical burns: In case of chemical burns i.e., due to acid and other chemicals, wash with running water for 10 minutes and then cover with dressing.

Question 3.
Describe the ways in which communicable diseases are transmitted through various indirect methods.
Answer:
Indirect methods of transmission of communicable diseases:

  1. Using items used by the infected persons: The healthy persons may be infected by using the articles like towel, hankey, utensils, bedding used by the patient infected by the communicable diseases. Diseases like tuberculosis, ring worm; common cold, influenza are transmitted by this method.
  2. Contaminated food and water: Diseases like dysentery, cholera spread through the contaminated food and water. Flies sitting on the food, if taken by a healthy person may be infected by the germs which may cause vomiting and loose motions. Similarly water and food infected by entamoeba may cause dysentery to persons who may take contaminated food.
  3. Vectors or carriers: Organisms like mosquitoes and house flies, ticks carry germs from the source of infection and pass on the germs to the normal persons and thus they are infected by diseases like malaria, cholera, plague. These organisms which carry the disease are called vectors and are not infected themselves.
    Mosquitoes suck blood and carry the disease causing protozoans from infected persons to healthy persons.
    Similarly houseflies carry the germs from garbage and sewage to the food. If this food is taken by the persons they become prey to typhoid and other diseases.
  4. Air: One sneeze from a person infected by cold may give billions of germs which are carried by air and may infect the healthy person. Tuberculosis passes from one person to other by coughing or sneezing of the infected person.
    These germs remain suspended in the air and persons may be infected by these spores or germs. Common cold, measles, diptheria, chicken pox.

Question 4.
Given a crossword puzzle. Read the clues across and clues downward, and fill up the blank squares. Check up your performance with the correct solution given at the end.

Clues across

  1. Category of pathogen that causes diseases, like common cold and mumps.
  2. These may readily grow in your hair, if you do not wash it regularly.
  3. This is the vaccine for preventing tuberculosis.
  4. Cover this part of your body by a handkerchief while sneezing to prevent droplet infection to others.
  5. The disease pertussis is popularly known as whooping
  6. One of the most common insects which visits our exposed foods and contaminates them.
  7. A disease that weakens body’s defence system
    Selina Concise Biology Class 8 ICSE Solutions – Diseases and First Aid 4
  8. Germ or germ – substance introduced into the body to prevent occurrence of an infectious disease.
  9. A disease in which the eyes, the skin and the urine turn yellow.
  10. An organ usually affected by tuberculosis.
  11. A disease caused by the bite of an infected dog, and which affects the central nervous system.

Answer:
Selina Concise Biology Class 8 ICSE Solutions – Diseases and First Aid 5

Selina Concise Biology Class 8 ICSE Solutions – Reproduction in Plants

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Selina Concise Biology Class 8 ICSE Solutions – Reproduction in Plants

ICSE SolutionsSelina ICSE SolutionsML Aggarwal Solutions

APlusTopper.com provides step by step solutions for Selina Concise ICSE Solutions for Class 8 Biology Chapter 2 Reproduction in Plants. You can download the Selina Concise Biology ICSE Solutions for Class 8 with Free PDF download option. Selina Publishers Concise Biology for Class 8 ICSE Solutions all questions are solved and explained by expert teachers as per ICSE board guidelines.

Selina Class 8 Biology ICSE SolutionsChemistryPhysicsMathsGeographyHistory & Civics

Selina Concise ICSE Solutions for Class 8 Biology Chapter 2 Reproduction in Plants

REVIEW QUESTIONS

Multiple Choice Questions:

1. Put a tick mark (✓) against the correct alternative in the following statements

(a) Pollen is produced in the:

  1. Filament
  2. Style
  3. Pistil
  4. Anther

(b) Reproductive whorls of a flower are:

  1. Stamens and carpels
  2. Sepals and petals
  3. Sepals and stamens
  4. Petals and carpels

(c) Grafting is a method of:

  1. Artificial vegetative propagation
  2. Sexual reproduction
  3. Artificial pollination
  4. Cross-pollination

(d) Which one of the following is a false fruit ?

  1. Tomato
  2. Apple
  3. Potato
  4. Pea

Short Answer Questions:

Question 1.
Write two ways in which pollination may occur in plants.
Answer:
The two ways in which pollination may occur in plants are:
(a) Self-pollination.
(b) Cross-pollination.

Question 2.
Name the three agents of pollination.
Answer:
The three agents of pollination are:
(a) Insect
(b) Wind
(c) Water

Question 3.
Give two features of flowers which favour pollination by insects.
Answer:
Specialities of insect-pollinated flowers:
(a) These flowers are large with coloured petals to attract insects.
(b) These are scented so that insects locate the flowers by smell.

Question 4.
Name two characteristics of flowers in which pollination occur by wind.
Answer:
Special features of wind-pollinated flowers:
(a) They produce light pollen so that it is easily carried away.
(b) They produce a large quantity of pollen.

Question 5.
What is a “false fruit” ? Give one example:
Answer:
In false fruits the base of the flowers (thalamus) becomes the main fleshy part of the fruit, while the ovary remains a small central part containing seeds. Example: Apple and Pear.

Question 6.
Name any three agencies for dispersal of seeds.
Answer:
a. Wind
b. Water
c. Man and animals, birds, bats, squirrels.

Question 7.
Fill in the blanks by selecting suitable words:
(unisexual, fertilisation, fruit, stamen, anther, bisexual, pollination, seed, ovary)
Answer:
a. A flower that bears both the male and the female parts is known as bisexual flower.
b. A flower bearing only male or female parts is known as unisexual flower.
c. Transfer of pollen grains from the anther to the stigma is known as pollination.
d. Fusion of male cell with the female cell is called fertilisation.
e. The ovule develops into a seed.
f. The ovary of the flower develops into a fruit.

Long Answer Questions:

Question 1.
What is vegetative reproduction?
Answer:
Vegetative reproduction: In this method, new plants are produced by the vegetative parts of the plants. The vegetative part mean the leaf, stem and root. Potato, mint, ginger, banana etc. are reproduced by this method.
Vegetative propagation can occur by natural methods as well as by artificial methods.
Natural method includes reproduction by stem, by roots and by leaves.
Artificial method include reproduction by cutting, layering, grafting and tissue culture.

Question 2.
Briefly explain why a gardener prefers to grow certain plants vegetatively?
Answer:
Gardener prefer to grow certain plants by vegetative method. The advantages in doing so are as follows:

  1. Reproduction by vegetative parts takes place in a shorter time.
  2. New plants, thus produced, spread very fast in a small area.
  3. It is a surer method.
  4. All the characters of the mother plant are retained by the daughter plants.

Question 3.
Why is it disadvantageous to grow plants vegetatively?
Answer:
It is disadvantageous to grow plants vegetatively because of following:

  1. As all plants developed by vegetative propagation are identical, they are likely to be affected simultaneously if a disease spreads in the farm.
  2. Dispersal of plants does not take place on its own. Daughter plants, so developed, tend to remain nearby and are restricted to a particular area leading to competition for resources.

Question 4.
What is meant by pollination? Explain the structure of germinating pollen grain with the help of a labelled diagram.
Answer:
Pollination: Pollination is the process in which the pollen grains from the anthers are transferred to the stigma.
Structure of the pollen grain: After pollination pollen grains are deposited on the stigma of the carpel. Under suitable conditions pollen grains produce a tube known as pollen tube. This tube grows down through the stigma and style towards the ovary.
Selina Concise Biology Class 8 ICSE Solutions – Reproduction in Plants 1
The nucleus of the pollen grains divides by mitosis and forms two male gametes. The tip of the pollen tube after entering ovary discharges the two male gametes into the embryo sac.
One of the male gametes fuses with the egg to form the zygote. This fusion is called fertilization. Another male gamete fuses with the diploid secondary nucleus and forms the endosperm, a food storing tissue.

Question 5.
Imagine all the seeds produced by a plant happen to fall under the same plant and sprout into new plants. Mention any two problems that will be faced by the new plants. –
Answer:
If all the seeds produced by a plant happen to fall under the same plant and sprout into new plants then in this situation plants will face the following problems:

  1. A large number of plants will grow in a small limited space. The water and the minerals available to them in the soil will be limited.
  2. The air surrounding them will not be enough and less sunshine will be available to them. As a result, most of these sprouted plants will die.

Question 6.
What is a flower ? Draw a neat labelled diagram showing the L.S. of a typical flower.
Answer:
A flower is a reproductive part of a plant. It helps in sexual reproduction as it has male parts and female parts. A fully opened flower has the following parts:
Selina Concise Biology Class 8 ICSE Solutions – Reproduction in Plants 2

Stalk—A flower is attached to the shoot by means of stalk or pedicel stalk. The tip of the stalk is swollen or flattened. This is called torus or thalamus or receptacle.
The different parts of a flower are inserted on the thalamus. There are usually four whorls as

Calyx (Sepals)
Corolla (Petals)
Androecium (stamens)
Gynoecium (Carpels) Present on the thalamus

  1. Sepals (Calyx): These are the outermost part of the flower. These are leaf like and green in colour. This is the outer covering of the flower and form outer whorl in a flower. The Calyx (sepals) enclose the inner parts of the flower when it is a bud. It is protective in function.
  2. Corolla (Petals): Petals form the second whorl inner to the sepals. These are usually coloured, gaudy, or white in colour and scented and give sweet smell. The value of a flower is due to the attractive colour of the petals. These attract the insects for pollination.
  3. Stamens (Androecium): The third whorls inner to the petals are stamens. This third whorl is called Androecium. These are the male parts of the flower. Each stamen is formed of a long narrow, hair like structure called filament. On its tip it bears, a rounded broad sac like structure called anther. Each anther has two anther lobes. Each anther lobe has two pollen sacs which have powdery mass called pollen grains.
  4. Carpels (Gynoecium): Carpels are the inner most or fourth whorl in a flower. It is lodged on the thalamus and forms the female part of a flower. This whorl of carpels is called gynoecium. Each carpel or pistil has three parts.
    (a) The lower most, swollen part is ovary. It is attached to the thalamus.
    (b) The middle part is style which is narrow, thread like.
    (c) Stigma: The style ends in a knob like, rounded structure which is sticky in nature to receive the pollen grains.
    The ovaries contain ovules which later turn into seeds after fertilization and the ovary wall forms the fruit sometimes the thalamus also becomes a part of the fruit as in apple.

Question 7.
Write short notes on the following:
(a) Micro propagation
(b) Bryophyllum
(c) Vegetative reproduction
(d) Grafting
Answer:
(a) Micro propagation: This is the propagation of plants involving cell and tissue culture. If vegetative propagation is not possible in a crop, then buds, shoot apex or any other part of the plant can be used as explant for micropropagation.
Selina Concise Biology Class 8 ICSE Solutions – Reproduction in Plants 3

  1. The explants are treated with sterilisation chemicals to prevent microbial growth, and then cultured in a particular nutrient medium.
  2. Cells grow and divide to form a cell mass called callus Some growth regulators (Plant hormones) are added.
  3. The callus differentiates into plant parts looking like plant (plantlet). After 4-6 weeks the plantlets transferred to the soil.

(b) Bryophyllum: It is a beautiful plant grown in gar xerophyte plant and can grow in any type soil or container. It requires sun and watering time to time. We can grow it vegetatively.
Selina Concise Biology Class 8 ICSE Solutions – Reproduction in Plants 4
When a leaf is put on the soil or falls off accidentally from the parent plant. It starts giving out buds in the notches of the leaves. These buds start growing when in touch with soil having moisture. They give out adventitious roots which go into the soil and small aerial shoots which go into the air. So these adventitious buds form many plants from a single plant. Thus we can get many plants from a single leaf. We can grow these tiny plants into separate pots to get independent plants. This is one of the vegetative mode of reproduction.

(c) Vegetative reproduction: This is method of producing new plants from the vegetative parts of the plants. The vegetative part means the leaf, stem, root. As potato, mint, ginger, banana, sugar beet, gul-e-daudi, asparagus, sugar cane, are produced by this method.

(d) Grafting: In plants like mango, zizyphus (ber), guava apples, fruits, roses, a small bud is fixed on the stem. Many types of apples on a single plant thus a small orchard on a single plant. So we can have different types of roses and chrysanthemums on a single plant.
Selina Concise Biology Class 8 ICSE Solutions – Reproduction in Plants 5

Question 8.
How artificial pollination is useful to plant breeders ? Discuss briefly.
Answer:
Artificial pollination means transfer of pollen to the stigma artificially. In ancient times, it was a common practice to sprinkle “male flowers of palms on the “female flowers”. However, in modem era, plant breeders use artificial pollination for developing new varieties. The breeders remove the anthers in young flowers and cover such flowers by plastic bags. Such flowers are then pollinated with pollen from the plants of the desired variety.

Question 9.
With the help of suitable diagrams, describe
(a) Binary fission in plants
(b) Budding in yeast cell
Answer:
(a) Binary fission: This is one of the asexual mean of reproduction. In lower plants like bacteria reproduction takes place by this process. In this process the nucleus of the cell divides into two. Then the cell wall splits across the middle of the cell. Thus each part has a nucleus. Thus each part is an independent bacterium.Selina Concise Biology Class 8 ICSE Solutions – Reproduction in Plants 6
Later on these two parts of the cell get separated from each other and form two independent individuals called daughter cells and lead independent life.

(b) Budding in yeast cell: Budding is the most common method in yeast. The Parent cell produces an outgrowth called a bud. The bud grows, and then gets detached from the parent body to lead an independent life.
Selina Concise Biology Class 8 ICSE Solutions – Reproduction in Plants 7

Selina Concise Biology Class 8 ICSE Solutions – The Circulatory System

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Selina Concise Biology Class 8 ICSE Solutions – The Circulatory System

ICSE SolutionsSelina ICSE SolutionsML Aggarwal Solutions

APlusTopper.com provides step by step solutions for Selina Concise ICSE Solutions for Class 8 Biology Chapter 6 The Circulatory System. You can download the Selina Concise Biology ICSE Solutions for Class 8 with Free PDF download option. Selina Publishers Concise Biology for Class 8 ICSE Solutions all questions are solved and explained by expert teachers as per ICSE board guidelines.

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Selina Concise ICSE Solutions for Class 8 Biology Chapter 6 The Circulatory System

REVIEW QUESTIONS

Multiple Choice Questions:

1. Put a tick mark (✓) against the correct alternative in the following statements:

(a) The only artery which carries deoxygenated blood is called,

  1. Hepatic artery
  2. Pulmonary artery
  3. Aorta
  4. Renal artery

(b) Pulmonary vein carries

  1. Oxygenated blood
  2. Deoxygenated blood
  3. Glucose-deficient blood
  4. CO2 laden blood

(c) Function of WBCs is to

  1. Transport oxygen
  2. Help in clotting of blood
  3. Provide immunity
  4. Provide storage of food.

(d) Blood Capillary is a

  1. Broad tube
  2. Artery with thick wall
  3. Vein with large lumen
  4. Narrow tube made up of endothelium only.

(e) Nucleus is absent in 

  1. RBCs
  2. WBCs
  3. All blood cells
  4. Liver cells.

(f) Sphygmomanometer measures

  1. Pulse rate
  2. Heart beat
  3. Blood pressure
  4. Brain activity

(g) The blood tastes saltish due to the presence of dissolved:

  1. Sodium chloride
  2. Potassium chloride
  3. Ammonium nitrate
  4. Sodium nitrate

Short Answer Questions:

Question 1.
1. Differentiate between the following pair of terms:
(a) Pulmonary artery and pulmonary vein.
(b) Vena cava and aorta.
(c) Platelets and WBC.
(d) RBC and WBC Ans.
Answer:
(a) Pulmonary artery and pulmonary vein.

Pulmonary arteryPulmonary vein
1. This involves circulation of blood from the heart to the lungs.1. This involves circulation of blood to the heart from the lungs.
2. It carries deoxygenated blood.2. It carries oxygenated blood.

(b) Vena cava and Aorta

Vena CavaAorta
1. Vena Cava is a large vein.1. Aorta is the large artery.
2. It carries deoxygenated blood from the upper and lower parts of the body i.e. head and shoulders.2. It carries oxygenated blood to all parts of the body through its branches.

(c) Blood platelets and blood group.

PlateletsWBC
1. These are colourless, oval or round, cytoplasmic fragments1. WBC are colourless and lack haemoglobin, larger in quantity, and have distinct oval and lobed nucleus.
2. These play a major role in blood clotting.2. They prevent body from disease causing germs by providing immunity
3. Their life span is 3-5 days and it is called thrombocytes.3. Their life span is short i.e. 5 to 20 days.

(d) RBC and WBC

RBCWBC
1. They do not have nucleus at maturity.1. They have a large characteristic nucleus.
2. They possess haemoglobin and are red.2. They are colourless as they have no pigment.
3. They help in transport of respiratory gases.3. They help in defence mechanism.

Question 2.
Give any three differences between an artery and a vein:
Answer:
Following are the differences between the artery and a vein:

ArteryVein
1. Arteries carry blood from the heart to various body parts.1. Veins carry blood from different body parts to the heart.
2. These carry oxygenated blood (except the pulmonary artery).2. These carry deoxygenated blood (except the pulmonary vein).
3. B lood flows with h igh speed and under high pressure.3. Blood flows with low speed and under low pressure.

Question 3.
Fill in the blanks with suitable words given below:
Answer:
a. The two lower chambers of the heart are called ventricles.
b. The pulmonary artery takes the blood from the ventricles to the lungs.
c. The blood loaded with carbon dioxide from the body comes into the right auricle of the heart.
d. The oxygen-rich blood from the lungs comes into the left ventricle of the heart.
e. The oxygen-rich blood is pumped into different parts of the body through aorta.
f. The carbon dioxide loaded blood from right ventricle is pumped into the lungs through pulmonary artery.
g. The instrument used to find out the blood pressure is known as sphygmomanometer.
h. The colour of a red blood cell is due to haemoglobin.
i. The blood plasma contains a dissolved substance called fibrinogen.
j. The liquid part of coagulated blood is known as serum.

Question 4.
In which organ of our body does blood get oxygenated?
Answer:
Blood becomes oxygenated in the lungs. The oxygenated blood is returned to left verticles by the pulmonary vein.

Question 5.
Which side of the heart (left or right) contains oxygenated blood?
Answer:
The left side of the heart contains oxygenated blood.

Question 6.
What is the role of haemoglobin in the blood ?
Answer:
The haemoglobin is the respiratory pigment which is formed of the iron containing part known as haemin and protein part known as globin. It helps to transport respiratory gases (oxygen).

Question 7.
Name the disease in which the number of platelets reduces to 25,000 – 30,000 per cubic mm of blood. State its major symptoms.
Answer:
Dengue fever is one such disease in which the number of platelets get reduced to as low as 25-30 thousands per cubic mm of blood. The major symptoms of dengue are high fever, rashes or red spots on body, nausea or vomiting, pain in abdomen, back, or back of the eyes and muscles.

Long Answer Questions:

Question 1.
 Given alongside is a diagram of human heart showing its internal structures. Label the parts marked 1 to 6, and answer the following questions.
Selina Concise Biology Class 8 ICSE Solutions – The Circulatory System 1
(a) Which type of blood is carried by the blood vessel marked 2?
(b) Name the main artery which takes the blood from heart to different parts of the body?
(c) Which chamber of the heart receives deoxygenated blood from the body?
Answer:

  1. Left pulmonary artery
  2. Superior vena cava
  3. Left pulmonary vein
  4. Right auricle
  5. Left auricle
  6. Left ventricle

(a) Deoxygentated blood.
(b) Aortic arch (Aorta).
(c) Right Atrium

Question 2.
You can see some blood vessels on the outside of the hands specially in older people. Are those veins or arteries ? How can you confirm your answer ?
Answer:
In older persons the skin becomes loose as the fat below becomes less with age and the vessels passing through these areas especially on the outside of the hands become prominent. These are veins as they flow superficially. The veins are thin and less muscular. These carry the blood to the heart veins are placed superficially so they are easily visible to the eye and are prominent.
The blood in the veins will be carrying CO2 and will have many substances like sugar, amino acids, chemicals and bacteria.

Question 3.
Give the functions of lymph. Differentiate between Blood and the lymph.
Answer:
Functions of lymph are:

  1. Nutritive: It supplies nutrition and oxygen to those parts where blood cannot reach.
  2. Drainage: It drains away excess tissue fluid and metabolites and returns proteins to the blood from tissue spaces.
  3. Absorption: It absorbs the fats from the intestine through lymphatics.
  4. Defence: Lymphocytes and monocytes of the lymph function to protect the body. The lymphatics also remove bacteria from the tissues.

Difference between Blood and Lymph

LymphBlood
1. It contains blood plasma without blood proteins and some RBC.1. It contains blood plasms with proteins and all three types of blood cells namely RBC, WBC and blood platelets.
2. They are light yellow in colour and does not contain RBC and haemoglobin.2. They are red in colour due to presence of haemoglobin in RBC,
3. It doesnot carry Oxygen.3. It carries oxygen in the body.
4. It is the part of open circulatory system.4. It is the part of closed circulatory system.

Question 4.
Name any two heart conditions that occur commonly. Briefly explain each of them.
Answer:

  1. Palpitations: Sometimes, one may experience the heart beating too hard or too fast or sometimes even skipping a beat. This can be frightening, but not serious or harmful and often this condition goes away on its own. Most of the time it is caused by stress or anxiety. Sometimes certain types of food may also cause palpitations.
    In rare cases, palpitations may be an indication of a more serious heart condition, specially if it is accompanied by shortness of breath, dizziness or chest pain.
  2. Hypertension: This is a condition that occurs in a person when blood flows through the blood vessels with a force greater than normal. This is also called High Blood Pressure. Hypertension can strain the heart, damage blood vessels and increase the risk of a heart attack or stroke.

Question 5.
During surgical operations or during accidents, the patient may be given blood from outside to save his life. What is the technical name of this process ? Briefly explain the precautions to be observed and taken in this process.
Answer:
During surgical operation or an accident when excess of bleeding takes place, the patient may be given blood from outside to save his life.
The transfer of blood from the donor to the recipient is called blood transfusion.
The following precautions are taken before the blood is given to the needy person:

  1. Matching of the donor’s blood with that of the recipient should be done.
  2. It should be made sure clinically that blood of donor is free from any infection.
  3. Sterilization of all the instruments to be used during the operation is must.

Question 6.
State briefly, the difference between white blood cells and the red blood cells.
Answer:
Difference between white blood cells and the red blood cells:

RBCWBC
1. They do not have nucleus at maturity.1. They have a large characteristic nucleus.
2. They possess haemoglobin and are red.2. They are colourless as they have no pigment.
3. They help in transport of respiratory gases.3. They help in defence mechanism.
4. Life span is 120 days.4. WBC have a short life span of 5 to 20 days.
5. They are about 5 million/mm3 of blood.5. They are about 7000/ mm3 of blood.
6. In the embryonic stage the RBC are formed in the liver and spleen. But after birth, they are formed in the red bone marrow.6. WBC are formed in the red bone marrow.

Question 7.
Answer very briefly, the following:
(a) Red Blood cells have no nucleus, then why do we call them cells?
(b) Why is it necessary to know The blood groups of the donor as well as the recipient ?
(c) Why should the blood going away from the stomach and intestines pass through the liver and not directly to heart?
Answer:
(a) RBC are formed in the liver and spleen when the organisjn is foetus. After birth these are formed in the red bone marrow. At the time of formation of RBC’s they have nucleus but later on they loose nucleus. Those enucleated cells perform all the functions of a cell so these are called cells.
RBC’s are surrounded by semipermeable plasma membrane. It contains homogenous cytoplasm and it is without the nucleus, endoplasmic reticulum, mitochondria, ribosomes and centrioles. RBC’s get advantage due to this condition. Corpuscles have more space to hold haemoglobin. It can as well give more oxygen by the haemoglobin to the tissue cells. So the enucleated condition is more useful to the tissue cells. The necessity of work has made them without nucleus and perform all the functions of the cells so they are called cells.

(b) Before transfusion of blood, it is most essential to determine the blood group of the donor and the recipient. The blood group of the donor and the recipient must match with each other, otherwise the RBC’s will stick to each other and thus the life of a recipient may be in danger as the blood groups are different. The sticking is due to the antigens (proteins) found in the blood of the donor and the antibodies found in the blood of the recipient.

(c) The blood from the stomach and the intestine goes to liver before going to the heart. Liver monitors the substances before passing into the body. Excess of glucose is retained by the liver in the form of glycogen and the excess amino acids are broken down by the liver. Harmful chemicals are detoxified and bacteria are destroyed and excess minerals, water and vitamins are stored in the liver.

Question 8.
Name the three kinds of blood vessels found in human beings. With the help of suitable diagrams, differentiate between them.
Answer:
The three kind of blood vessels found in human beings are arteries, veins and capillaries.

  1. Arteries are the blood vessels that carry blood from the heart to the various parts of the body.
  2. Veins are the blood vessels that carry blood from the body parts to the heart.
  3. Capillaries: These are the terminal branches of an artery, which rejoin to form a vein. A capillary is a very narrow tube whose walls have a single layer of cells with no muscles. Although the wall of a capillary is veiy thin, yet an exchange of nutrients, waste products and gases take place between the blood and the body fluids.Selina Concise Biology Class 8 ICSE Solutions – The Circulatory System 2

Differences:

Arteries

  1. Carry blood away from the heart.
  2. Have thick and more muscular walls.
  3. Carry oxygenated blood (except pulmonary artery which carries deoxygenated blood).
  4. The blood flows with jerks and under great force.

Veins

  1. Carry blood towards the heart.
  2. Have thin and less muscular walls.
  3. Carry deoxygenated blood (except pulmonary vein which carries oxygenated blood).
  4. The blood flows smoothly and under little pressure.

Capillaries:

  1. Arteries after entering an organ divide into number of smaller branches called arterioles which further divide repeatedly to form a network of fine branches called capillaries.
  2. The walls of the capillaries are very thin and are one cell deep.
  3. The Capillaries after the metabolic exchange unite to form larger vessels called venules, which again unite to form a vein.

Selina Concise Mathematics Class 8 ICSE Solutions Chapter 1 Rational Numbers

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Selina Concise Mathematics Class 8 ICSE Solutions Chapter 1 Rational Numbers

Selina Publishers Concise Mathematics Class 8 ICSE Solutions Chapter 1 Rational Numbers

ICSE SolutionsSelina ICSE SolutionsML Aggarwal Solutions

APlusTopper.com provides step by step solutions for Selina Concise ICSE Solutions for Class 8 Mathematics Chapter 1 Rational Numbers. You can download the Selina Concise Mathematics ICSE Solutions for Class 8 with Free PDF download option. Selina Publishers Concise Mathematics for Class 8 ICSE Solutions all questions are solved and explained by expert mathematic teachers as per ICSE board guidelines.

Selina Class 8 Maths SolutionsPhysicsChemistryBiologyGeographyHistory & Civics

Rational Numbers Exercise 1A – Selina Concise Mathematics Class 8 ICSE Solutions

Question 1.
Add, each pair of rational numbers, given below, and show that their addition (sum) is also a rational number:
Selina Concise Mathematics Class 8 ICSE Solutions Chapter 1 Rational Numbers image - 1
Solution:
Selina Concise Mathematics Class 8 ICSE Solutions Chapter 1 Rational Numbers image - 2
Selina Concise Mathematics Class 8 ICSE Solutions Chapter 1 Rational Numbers image - 3
Selina Concise Mathematics Class 8 ICSE Solutions Chapter 1 Rational Numbers image - 4
Selina Concise Mathematics Class 8 ICSE Solutions Chapter 1 Rational Numbers image - 5
Selina Concise Mathematics Class 8 ICSE Solutions Chapter 1 Rational Numbers image - 6
Selina Concise Mathematics Class 8 ICSE Solutions Chapter 1 Rational Numbers image - 7

Question 2.
Evaluate:
Selina Concise Mathematics Class 8 ICSE Solutions Chapter 1 Rational Numbers image - 8
Solution:
Selina Concise Mathematics Class 8 ICSE Solutions Chapter 1 Rational Numbers image - 9
Selina Concise Mathematics Class 8 ICSE Solutions Chapter 1 Rational Numbers image - 10
Selina Concise Mathematics Class 8 ICSE Solutions Chapter 1 Rational Numbers image - 11
Selina Concise Mathematics Class 8 ICSE Solutions Chapter 1 Rational Numbers image - 12
Selina Concise Mathematics Class 8 ICSE Solutions Chapter 1 Rational Numbers image - 13
Selina Concise Mathematics Class 8 ICSE Solutions Chapter 1 Rational Numbers image - 14

Question 3.
Evaluate:
Selina Concise Mathematics Class 8 ICSE Solutions Chapter 1 Rational Numbers image - 15
Solution:
Selina Concise Mathematics Class 8 ICSE Solutions Chapter 1 Rational Numbers image - 16
Selina Concise Mathematics Class 8 ICSE Solutions Chapter 1 Rational Numbers image - 17
Selina Concise Mathematics Class 8 ICSE Solutions Chapter 1 Rational Numbers image - 18
Selina Concise Mathematics Class 8 ICSE Solutions Chapter 1 Rational Numbers image - 20
Selina Concise Mathematics Class 8 ICSE Solutions Chapter 1 Rational Numbers image - 22

Question 4.
For each pair of rational numbers, verify commutative property of addition of rational numbers:
Selina Concise Mathematics Class 8 ICSE Solutions Chapter 1 Rational Numbers image - 23
Solution:
Selina Concise Mathematics Class 8 ICSE Solutions Chapter 1 Rational Numbers image - 24
This verifies the commutative property for the addition of rational numbers.
Selina Concise Mathematics Class 8 ICSE Solutions Chapter 1 Rational Numbers image - 25
Selina Concise Mathematics Class 8 ICSE Solutions Chapter 1 Rational Numbers image - 26
This verifies the commutative property for the addition of rational numbers.
Selina Concise Mathematics Class 8 ICSE Solutions Chapter 1 Rational Numbers image - 27
Selina Concise Mathematics Class 8 ICSE Solutions Chapter 1 Rational Numbers image - 28
This verifies the commutative property for the addition of rational numbers.
Selina Concise Mathematics Class 8 ICSE Solutions Chapter 1 Rational Numbers image - 29
This verifies the commutative property for the addition of rational numbers.
Selina Concise Mathematics Class 8 ICSE Solutions Chapter 1 Rational Numbers image - 30
This verifies the commutative property for the addition of rational numbers.
Selina Concise Mathematics Class 8 ICSE Solutions Chapter 1 Rational Numbers image - 31
Selina Concise Mathematics Class 8 ICSE Solutions Chapter 1 Rational Numbers image - 32
This verifies the commutative property for the addition of rational numbers.

Question 5.
For each set of rational numbers, given below, verify the associative property of addition of rational numbers:
Selina Concise Mathematics Class 8 ICSE Solutions Chapter 1 Rational Numbers image - 33
Solution:
Selina Concise Mathematics Class 8 ICSE Solutions Chapter 1 Rational Numbers image - 34
Selina Concise Mathematics Class 8 ICSE Solutions Chapter 1 Rational Numbers image - 35
This verifies associative property of the addition of rational numbers.
Selina Concise Mathematics Class 8 ICSE Solutions Chapter 1 Rational Numbers image - 36
Selina Concise Mathematics Class 8 ICSE Solutions Chapter 1 Rational Numbers image - 37
This verifies associative property of the addition of rational numbers.
Selina Concise Mathematics Class 8 ICSE Solutions Chapter 1 Rational Numbers image - 38
Selina Concise Mathematics Class 8 ICSE Solutions Chapter 1 Rational Numbers image - 39
Selina Concise Mathematics Class 8 ICSE Solutions Chapter 1 Rational Numbers image - 40
This verifies associative property of the addition of rational numbers.
Selina Concise Mathematics Class 8 ICSE Solutions Chapter 1 Rational Numbers image - 41
Selina Concise Mathematics Class 8 ICSE Solutions Chapter 1 Rational Numbers image - 42

Question 6.
Write the additive inverse (negative) of:
Selina Concise Mathematics Class 8 ICSE Solutions Chapter 1 Rational Numbers image - 43
Solution:
Selina Concise Mathematics Class 8 ICSE Solutions Chapter 1 Rational Numbers image - 44

Question 7.
Fill in the blanks:
Selina Concise Mathematics Class 8 ICSE Solutions Chapter 1 Rational Numbers image - 45
Solution:
Selina Concise Mathematics Class 8 ICSE Solutions Chapter 1 Rational Numbers image - 46
Selina Concise Mathematics Class 8 ICSE Solutions Chapter 1 Rational Numbers image - 47

Question 8.
State, true or false:
Selina Concise Mathematics Class 8 ICSE Solutions Chapter 1 Rational Numbers image - 48
Solution:
(i) False
(ii) False
(iii) True
(iv) True
(v) False
(vi) False

Rational Numbers Exercise 1B – Selina Concise Mathematics Class 8 ICSE Solutions

Question 1.
Evaluate:
Selina Concise Mathematics Class 8 ICSE Solutions Chapter 1 Rational Numbers image - 49
Solution:
Selina Concise Mathematics Class 8 ICSE Solutions Chapter 1 Rational Numbers image - 50
Selina Concise Mathematics Class 8 ICSE Solutions Chapter 1 Rational Numbers image - 51
Selina Concise Mathematics Class 8 ICSE Solutions Chapter 1 Rational Numbers image - 52
Selina Concise Mathematics Class 8 ICSE Solutions Chapter 1 Rational Numbers image - 53

Question 2.
Subtract:
Selina Concise Mathematics Class 8 ICSE Solutions Chapter 1 Rational Numbers image - 54
Solution:
Selina Concise Mathematics Class 8 ICSE Solutions Chapter 1 Rational Numbers image - 55
Selina Concise Mathematics Class 8 ICSE Solutions Chapter 1 Rational Numbers image - 56
Selina Concise Mathematics Class 8 ICSE Solutions Chapter 1 Rational Numbers image - 57
Selina Concise Mathematics Class 8 ICSE Solutions Chapter 1 Rational Numbers image - 58

Question 3.
The sum of two rational numbers is \(\frac { 9 }{ 20 }\). If one of them is \(\frac { 2 }{ 5 }\), find the other.
Solution:
The sum of two rational numbers = \(\frac { 9 }{ 20 }\)
And, one of the numbers = \(\frac { 2 }{ 5 }\)
The other rational number
Selina Concise Mathematics Class 8 ICSE Solutions Chapter 1 Rational Numbers image - 59

Question 4.
The sum of the two rational numbers is \(\frac { -2 }{ 3 }\). If one of them is \(\frac { -8 }{ 5 }\), find the other.
Solution:
Selina Concise Mathematics Class 8 ICSE Solutions Chapter 1 Rational Numbers image - 60
Selina Concise Mathematics Class 8 ICSE Solutions Chapter 1 Rational Numbers image - 61

Question 5.
The sum of the two rational numbers is -6. If one of them is \(\frac { -8 }{ 5 }\), find the other.
Solution:
Selina Concise Mathematics Class 8 ICSE Solutions Chapter 1 Rational Numbers image - 62

Question 6.
Which rational number should be added to \(\frac { -7 }{ 8 }\) to get \(\frac { 5 }{ 9 }\) ?
Solution:
Selina Concise Mathematics Class 8 ICSE Solutions Chapter 1 Rational Numbers image - 63

Question 7.
Which rational number should be added to \(\frac { -5 }{ 9 }\) to get \(\frac { -2 }{ 3 }\) ?
Solution:
Selina Concise Mathematics Class 8 ICSE Solutions Chapter 1 Rational Numbers image - 64

Question 8.
Which rational number should be subtracted from \(\frac { -5 }{ 6 }\) to get \(\frac { 4 }{ 9 }\) ?
Solution:
Selina Concise Mathematics Class 8 ICSE Solutions Chapter 1 Rational Numbers image - 65

Question 9.
(i) What should be subtracted from -2 to get \(\frac { 3 }{ 8 }\)
(ii) What should be added to -2 to get \(\frac { 3 }{ 8 }\)
Solution:
Selina Concise Mathematics Class 8 ICSE Solutions Chapter 1 Rational Numbers image - 66
Selina Concise Mathematics Class 8 ICSE Solutions Chapter 1 Rational Numbers image - 67

Question 10.
Evaluate:
Selina Concise Mathematics Class 8 ICSE Solutions Chapter 1 Rational Numbers image - 68
Selina Concise Mathematics Class 8 ICSE Solutions Chapter 1 Rational Numbers image - 69
Solution:
Selina Concise Mathematics Class 8 ICSE Solutions Chapter 1 Rational Numbers image - 70
Selina Concise Mathematics Class 8 ICSE Solutions Chapter 1 Rational Numbers image - 71
Selina Concise Mathematics Class 8 ICSE Solutions Chapter 1 Rational Numbers image - 72

Rational Numbers Exercise 1C – Selina Concise Mathematics Class 8 ICSE Solutions

Question 1.
Evaluate:
Selina Concise Mathematics Class 8 ICSE Solutions Chapter 1 Rational Numbers image - 73
Solution:
Selina Concise Mathematics Class 8 ICSE Solutions Chapter 1 Rational Numbers image - 74
Selina Concise Mathematics Class 8 ICSE Solutions Chapter 1 Rational Numbers image - 75

Question 2.
Multiply:
Selina Concise Mathematics Class 8 ICSE Solutions Chapter 1 Rational Numbers image - 76
Solution:
Selina Concise Mathematics Class 8 ICSE Solutions Chapter 1 Rational Numbers image - 77
Selina Concise Mathematics Class 8 ICSE Solutions Chapter 1 Rational Numbers image - 78

Question 3.
Evaluate:
Selina Concise Mathematics Class 8 ICSE Solutions Chapter 1 Rational Numbers image - 79
Solution:
Selina Concise Mathematics Class 8 ICSE Solutions Chapter 1 Rational Numbers image - 80
Selina Concise Mathematics Class 8 ICSE Solutions Chapter 1 Rational Numbers image - 81
Selina Concise Mathematics Class 8 ICSE Solutions Chapter 1 Rational Numbers image - 82
Selina Concise Mathematics Class 8 ICSE Solutions Chapter 1 Rational Numbers image - 83

Question 4.
Multiply each rational number, given below, by one (1):
Selina Concise Mathematics Class 8 ICSE Solutions Chapter 1 Rational Numbers image - 84
Solution:
Selina Concise Mathematics Class 8 ICSE Solutions Chapter 1 Rational Numbers image - 85
Selina Concise Mathematics Class 8 ICSE Solutions Chapter 1 Rational Numbers image - 86

Question 5.
For each pair of rational numbers, given below, verify that the multiplication is commutative:
Selina Concise Mathematics Class 8 ICSE Solutions Chapter 1 Rational Numbers image - 87
Solution:
Selina Concise Mathematics Class 8 ICSE Solutions Chapter 1 Rational Numbers image - 88
Selina Concise Mathematics Class 8 ICSE Solutions Chapter 1 Rational Numbers image - 89

Question 6.
Write the reciprocal (multiplicative inverse) of each rational number, given below :
Selina Concise Mathematics Class 8 ICSE Solutions Chapter 1 Rational Numbers image - 90
Solution:
Selina Concise Mathematics Class 8 ICSE Solutions Chapter 1 Rational Numbers image - 91

Question 7.
Find the reciprocal (multiplicative inverse) of:
Selina Concise Mathematics Class 8 ICSE Solutions Chapter 1 Rational Numbers image - 92
Selina Concise Mathematics Class 8 ICSE Solutions Chapter 1 Rational Numbers image - 93
Solution:
Selina Concise Mathematics Class 8 ICSE Solutions Chapter 1 Rational Numbers image - 94

Question 8.
Selina Concise Mathematics Class 8 ICSE Solutions Chapter 1 Rational Numbers image - 95
Solution:
Selina Concise Mathematics Class 8 ICSE Solutions Chapter 1 Rational Numbers image - 96
Selina Concise Mathematics Class 8 ICSE Solutions Chapter 1 Rational Numbers image - 97

Question 9.
Selina Concise Mathematics Class 8 ICSE Solutions Chapter 1 Rational Numbers image - 98
Solution:
Selina Concise Mathematics Class 8 ICSE Solutions Chapter 1 Rational Numbers image - 99
Selina Concise Mathematics Class 8 ICSE Solutions Chapter 1 Rational Numbers image - 100

Question 10.
Name the multiplication property of rational numbers shown below :
Selina Concise Mathematics Class 8 ICSE Solutions Chapter 1 Rational Numbers image - 101
Solution:
(i) Commutativity property.
(ii) Associativity property.
(iii) Distributivity property.
(iv) Existence of inverse.
(v) Existence of identity.
(vi) Existence of inverse.

Question 11.
Fill in the blanks:
(i) The product of two positive rational numbers is always ……………
(ii) The product of two negative rational numbers is always ……………
(iii) If two rational numbers have opposite signs then their product is always …………..
(iv) The reciprocal of a positive rational number is ………. and the reciprocal of a negative raitonal number is ……………
(v) Rational number 0 has ………….. reciprocal.
(vi) The product of a rational number and its reciprocal is ………..
(vii) The numbers ……….. and ……….. are their own reciprocals.
(viii) If m is reciprocal of n, then the reciprocal of n is ………….
Solution:
(i) The product of two positive rational numbers is always positive.
(ii) The product of two negative rational numbers is always positive.
(iii) If two rational numbers have opposite signs then their product is always negative.
(iv) The reciprocal of a positive rational number is positive and the reciprocal of a negative raitonal number is negative.
(v) Rational number 0 has no reciprocal.
(vi) The product of a rational number and its reciprocal is 1.
(vii) The numbers 1 and -1 are their own reciprocals.
(viii)If m is reciprocal of n, then the reciprocal of n is m.

Rational Numbers Exercise 1D – Selina Concise Mathematics Class 8 ICSE Solutions

Question 1.
Evaluate:
Selina Concise Mathematics Class 8 ICSE Solutions Chapter 1 Rational Numbers image - 102
Selina Concise Mathematics Class 8 ICSE Solutions Chapter 1 Rational Numbers image - 103
Solution:
Selina Concise Mathematics Class 8 ICSE Solutions Chapter 1 Rational Numbers image - 104
Selina Concise Mathematics Class 8 ICSE Solutions Chapter 1 Rational Numbers image - 105
Selina Concise Mathematics Class 8 ICSE Solutions Chapter 1 Rational Numbers image - 106
Selina Concise Mathematics Class 8 ICSE Solutions Chapter 1 Rational Numbers image - 107

Question 2.
Divide:
Selina Concise Mathematics Class 8 ICSE Solutions Chapter 1 Rational Numbers image - 108
Solution:
Selina Concise Mathematics Class 8 ICSE Solutions Chapter 1 Rational Numbers image - 109
Selina Concise Mathematics Class 8 ICSE Solutions Chapter 1 Rational Numbers image - 110

Question 3.
The product of two rational numbers is -2. If one of them is \(\frac { 4 }{ 7 }\), find the other.
Solution:
Selina Concise Mathematics Class 8 ICSE Solutions Chapter 1 Rational Numbers image - 111

Question 4.
The product of two numbers is \(\frac { -4 }{ 9 }\). If one of them is \(\frac { -2 }{ 27 }\), find the other.
Solution:
Selina Concise Mathematics Class 8 ICSE Solutions Chapter 1 Rational Numbers image - 112

Question 5.
m and n are two rational numbers such that
Selina Concise Mathematics Class 8 ICSE Solutions Chapter 1 Rational Numbers image - 113
Solution:
Selina Concise Mathematics Class 8 ICSE Solutions Chapter 1 Rational Numbers image - 114

Question 6.
By what number must \(\frac { -3 }{ 4 }\) be multiplied so that the product is \(\frac { -9 }{ 16 }\) ?
Solution:
Selina Concise Mathematics Class 8 ICSE Solutions Chapter 1 Rational Numbers image - 115

Question 7.
By what number should \(\frac { -8 }{ 13 }\) be multiplied to get 16?
Solution:
Selina Concise Mathematics Class 8 ICSE Solutions Chapter 1 Rational Numbers image - 116

Question 8.
If 3\(\frac { 1 }{ 2 }\) litres of milk costs ₹49, find the cost of one litre of milk?
Solution:
Selina Concise Mathematics Class 8 ICSE Solutions Chapter 1 Rational Numbers image - 117

Question 9.
Cost of 3\(\frac { 2 }{ 5 }\) metre of cloth is ₹88\(\frac { 1 }{ 2 }\). What is the cost of 1 metre of cloth?
Solution:
Selina Concise Mathematics Class 8 ICSE Solutions Chapter 1 Rational Numbers image - 118

Question 10.
Divide the sum of \(\frac { 3 }{ 7 }\) and \(\frac { -5 }{ 14 }\) by \(\frac { -1 }{ 2 }\).
Solution:
Selina Concise Mathematics Class 8 ICSE Solutions Chapter 1 Rational Numbers image - 119
Selina Concise Mathematics Class 8 ICSE Solutions Chapter 1 Rational Numbers image - 120

Question 11.
Selina Concise Mathematics Class 8 ICSE Solutions Chapter 1 Rational Numbers image - 121
Solution:
Selina Concise Mathematics Class 8 ICSE Solutions Chapter 1 Rational Numbers image - 122
Selina Concise Mathematics Class 8 ICSE Solutions Chapter 1 Rational Numbers image - 123
Selina Concise Mathematics Class 8 ICSE Solutions Chapter 1 Rational Numbers image - 124

Question 12.
The product of two rational numbers is -5. If one of these numbers is \(\frac { -7 }{ 15 }\), find the other.
Solution:
Selina Concise Mathematics Class 8 ICSE Solutions Chapter 1 Rational Numbers image - 125
Selina Concise Mathematics Class 8 ICSE Solutions Chapter 1 Rational Numbers image - 126

Question 13.
Selina Concise Mathematics Class 8 ICSE Solutions Chapter 1 Rational Numbers image - 127
Solution:
Selina Concise Mathematics Class 8 ICSE Solutions Chapter 1 Rational Numbers image - 128
Selina Concise Mathematics Class 8 ICSE Solutions Chapter 1 Rational Numbers image - 129

Rational Numbers Exercise 1E – Selina Concise Mathematics Class 8 ICSE Solutions

Question 1.
Selina Concise Mathematics Class 8 ICSE Solutions Chapter 1 Rational Numbers image - 130
Solution:
Selina Concise Mathematics Class 8 ICSE Solutions Chapter 1 Rational Numbers image - 131

Question 2.
Selina Concise Mathematics Class 8 ICSE Solutions Chapter 1 Rational Numbers image - 132
Solution:
Selina Concise Mathematics Class 8 ICSE Solutions Chapter 1 Rational Numbers image - 133

Question 3.
Insert one rational number between (0 7 and 8 (ii) 3.5 and 5
(i) 2 and 3.2
(ii) 3.5 and 5
(iii) 2 and 3.2
(iv) 4.2 and 3.6
(v) \(\frac { 1 }{ 2 }\) and 2
Solution:
Selina Concise Mathematics Class 8 ICSE Solutions Chapter 1 Rational Numbers image - 134
Selina Concise Mathematics Class 8 ICSE Solutions Chapter 1 Rational Numbers image - 135

Question 4.
Insert two rational numbers between
(i) 6 and 7
(ii) 4.8 and 6
(iii) 2.7 and 6.3
Solution:
Selina Concise Mathematics Class 8 ICSE Solutions Chapter 1 Rational Numbers image - 136
Selina Concise Mathematics Class 8 ICSE Solutions Chapter 1 Rational Numbers image - 137
Selina Concise Mathematics Class 8 ICSE Solutions Chapter 1 Rational Numbers image - 138

Question 5.
Insert three rational numbers between
(i) 3 and 4
(ii) 10 and 12
Solution:
Selina Concise Mathematics Class 8 ICSE Solutions Chapter 1 Rational Numbers image - 139

Question 6.
Insert five rational numbers between \(\frac { 3 }{ 5 }\) and \(\frac { 2 }{ 5 }\)
Solution:
LCM of denominators 5 and 3 is 15
Selina Concise Mathematics Class 8 ICSE Solutions Chapter 1 Rational Numbers image - 140

Question 7.
Insert six rational numbers between \(\frac { 5 }{ 6 }\) and \(\frac { 8 }{ 9 }\)
Solution:
Selina Concise Mathematics Class 8 ICSE Solutions Chapter 1 Rational Numbers image - 141
Selina Concise Mathematics Class 8 ICSE Solutions Chapter 1 Rational Numbers image - 142

Question 8.
Insert seven rational numbers between 2 and 3.
Solution:
Selina Concise Mathematics Class 8 ICSE Solutions Chapter 1 Rational Numbers image - 143