NCERT Solutions for Class 8 Science Chapter 18 Pollution Of Air And Water are provided here with simple step-by-step explanations. These solutions for Pollution Of Air And Water are extremely popular among Class 8 students for Science Pollution Of Air And Water Solutions come handy for quickly completing your homework and preparing for exams. All questions and answers from the NCERT Book of Class 8 Science Chapter 18 are provided here for you for free. You will also love the ad-free experience on Meritnation’s NCERT Solutions. All NCERT Solutions for class Class 8 Science are prepared by experts and are 100% accurate.

Page No 104:

Question 1:

Air is a mixture of various gases. One of the gases is 21% part of the air and is essential for the survival of human beings. This gas is
(a) nitrogen             (c) ozone
(b) oxygen             (d) argon

Answer:

The gas that is 21% part of the air and essential for the survival of human beings is oxygen.

Hence, the correct answer is option (b).

Page No 104:

Question 2:

Which of the following is not a source of air pollution?
(a) automobile exhaust          (c) windmill
(b) burning of firewood        (d) power plant

Answer:

Windmill is not a source of air pollution. It is regarded as an alternative source of energy which uses sped of winds to generate energy.

Hence, the correct answer is option (c).

Page No 104:

Question 3:

Boojho wishes to contribute in reducing air pollution. Which vehicle should he use for going to school?
(a) car                      (c) autorickshaw
(b) school bus          (d) scooter

Answer:

Boojho should use a school bus to reduce air pollution.

Hence, the correct answer is option (b).

Page No 104:

Question 4:

Which of the following is not a way to conserve water?
(a) replace       (c) reuse
(b) reduce        (d) recycle

Answer:

Reduce, reuse and recycle is the mantra to save water conciously at the individual level.Replace is not a way to conserve water. 

Hence, the correct answer is option (a).

Page No 104:

Question 5:

The type of pollution which is likely to affect Taj Mahal in Agra to a greater extent is
(a) air pollution           (c) soil pollution
(b) water pollution      (d) noise pollution

Answer:

Air pollution is affecting Taj Mahal by corroding it and turning its white marble pale yellow.

Hence, the correct answer is option (a).

Page No 104:

Question 6:

Incomplete combustion of fuel such as petrol and diesel gives
(a) nitrogen oxide         (c) carbon monoxide
(b) sulphur dioxide       (d) carbon dioxide

Answer:

Carbon monoxide is produced by the incomplete combustion of fuels like wood, coal, kerosene, petrol and diesel.

Hence, the correct answer is option (c).

Page No 104:

Question 7:

The phenomenon of marble cancer is due to
(a) soot particles        (c) fog
(b) CFCs                   (d) acid rain

Answer:

The phenomenon of marble cancer Is due to acid rain. Marble cancer is corrosion of buildings or monuments by acid rain.

​Hence, the correct answer is option (d).

Page No 104:

Question 8:

Potable water is the water which is
(a) obtained from a river.       (c) pure and fit for drinking.
(b) obtained from a lake.        (d) used only for washing clothes.

Answer:

Water which is suitable for drinking is called potable water.

Hence, the correct answer is option C.



Page No 105:

Question 9:

Which of the following procedures will give you water free from all impurities?
(a) adding chlorine tablets        (c) boiling
(b) distillation                           (d) filtration

Answer:

Distillation removes nearly all the impurities like dissolved minerals, inorganic salts, heavy metals and bacteria from water.

Hence, the correct answer is option B.

Page No 105:

Question 10:

A pond contains clean water. Which of the following activities will produce least pollution of water?
(a) washing clothes in the pond
(b) animals bathing in the pond
(c) washing motor vehicles in the pond
(d) swimming in the pond.

Answer:

Swimming in the pond will produce least pollution of water because hazardous chemicals, gases and sewage are least likely to be mixed with water during this activity.

Hence, the correct answer is option D.

Page No 105:

Question 11:

Trees help in reducing the pollution of our environment. Lakhs of trees are planted by people in the month of July every year. The occasion is called
(a) forest Conservation Day        (c) Van Mahotsav
(b) plantation month                   (d) wildlife week

Answer:

Lakhs of trees are planted in July every year. This occasion is known as Van Mahotsav.

Hence, the correct answer is option C.

Page No 105:

Question 12:

Which of the following is not a green house gas?
(a) nitrogen gas         (c) methane gas
(b) water vapour       (d) carbon dioxide

Answer:

Nitrogen gas is the major component of air at about 78% but it is not a greenhouse gas. Gases like carbon dioxide, methane, nitrous oxide and water vapour are greenhouse gases.

Hence, the correct answer is option A.

Page No 105:

Question 13:

Name the chemicals which are used in refrigerators and air conditioners and damage ozone layer when released in air.

Answer:

Chlorofluorocarbons (CFCs) are used in refrigerators and air conditioners. They damage the ozone layer of the atmosphere.

Page No 105:

Question 14:

Name any two sources which cause air pollution due to suspended particulate matter.

Answer:

Two sources which cause air pollution due to suspended particulate matter are:

  • Burning of diesel and petrol by automobiles
  • Industrial processes like steel making and mining

Page No 105:

Question 15:

Name two gases which are mainly responsible for acid rain.

Answer:

Sulphur dioxide and nitrogen dioxide gases react with the water vapour present in the atmosphere to form sulphuric acid and nitric acid which makes the rain acidic.

Page No 105:

Question 16:

The quality of air at various locations is monitored regularly by government and other agencies. In what way can you use these data?

Answer:

We can use this data to create awareness about air pollution among family, friends and neighbours.

Page No 105:

Question 17:

Combustion of fossil fuels generates a lot of air pollution. Can you suggest any two alternative sources of energy which do not cause any pollution?

Answer:

Solar energy and wind energy are the two alternative sources of energy which do not cause any pollution.

Page No 105:

Question 18:

Name any two water pollutants which are toxic for plants and animals.

Answer:

Arsenic and lead are the two water pollutants which are toxic for plants and animals.



Page No 106:

Question 19:

A lot of dry leaves are collected in a school garden and are burnt every day. Do you think that it is right to do so? If not, what should be done to dispose off the dry leaves?

Answer:

No, it is not right to burn dry leaves because it leads to air pollution causing breathing problems. Alternatively, they should be put in a compost pit as they are biodegradable and will be converted into manure to be used for crops.

Page No 106:

Question 20:

The level of air pollution is higher at a busy traffic intersection. Why?

Answer:

At a busy traffic intersection, large number of vehicles stop for a short time and release high levels of pollutants like carbon monoxide, carbon dioxide, nitrogen oxides and smoke. Therefore, the level of air pollution is higher at a busy traffic intersection.

Page No 106:

Question 21:

Fill in the blanks with the help of words given in bracket after each sentence.
(a) When air is contaminated by ________ substances which have a ________ effect on both the ________ and ________, it is referred to as ________.
(air pollution, harmful, living, unwanted, non-living, pollutants).
(b) Many ________ are responsible for causing ________ pollution. Petroleum ________ are a major source of ________ pollutants like ________ and ________.
(sulphur dioxide, refineries, industries, nitrogen dioxide, gaseous, liquid, people, air).
(c) While ________ your teeth, leaving the ________ running may waste several ________ of water.
(tap, litres, brushing, washing, drops)
(d) Water which is suitable for _________ is called ________ water.
(washing, bathing, drinking, potable, soft).
(e) Water which looks clean still has disease carrying ________ and ________ impurities.
(insects, microorganism, particles, dissolved, harmful).

Answer:

(a) When air is contaminated by unwanted substances which have a harmful effect on both the living and non-living, it is referred to as air pollution.
(b) Many industries are responsible for causing air pollution. Petroleum refineries are a major source of gaseous pollutants like sulphur dioxide and nitrogen dioxide.
(c) While brushing your teeth, leaving the tap running may waste several litres of water.
(d) Water which is suitable for drinking is called potable water.
(e) Water which looks clean still has disease carrying microorganisms and dissolved impurities.

Page No 106:

Question 22:

Match the items of Column A with those of Column B.
Column A                                         Column B
(a) sulphur dioxide                 (i) damage ozone layer
(b) carbon dioxide                 (ii) reduces oxygen carrying capacity of blood
(c) carbon monoxide             (iii) acid rain.
(d) chlorofluorocarbons        (iv) green house gas

Answer:

Column A                                         Column B
(a) sulphur dioxide                 (iii) acid rain
(b) carbon dioxide                 (iv) green house gas
(c) carbon monoxide             (ii) reduces oxygen carrying capacity of blood
(d) chlorofluorocarbons        (i) damage ozone layer



Page No 107:

Question 23:

Find out the wrong statements and write them in their correct form.
(a) We can survive for some time without air but we cannot survive even for a few minutes without food.
(b) A brick kiln emits lot of smoke and other harmful gases causing air pollution.
(c) Carbon monoxide is produced by complete burning of fuels such as coal, petrol, diesel.
(d) Chlorination is a commonly used chemical method for killing germs in water.
(e) Water which is suitable for drinking is called soft water.

Answer:

The wrong statements are:
(a) We can survive for some time without air but we cannot survive even for a few minutes without food.
(c) Carbon monoxide is produced by complete burning of fuels such as coal, petrol, diesel.
(e) Water which is suitable for drinking is called soft water.

The corrected from of wrong statements are:
(a) We can survive for some time without food but we cannot survive even for a few minutes without air.
(c) Carbon monoxide is produced by incomplete burning of fuels such as coal, petrol, diesel.
(e) Water which is suitable for drinking is called potable water.

Page No 107:

Question 24:

In the following statements, the underlined words are jumbled up. Write them in their correct form.
(a) Air contains 78% ginroten and 21% gonexy.
(b) Vehicles produce high level of pollutants like carbon dioxide, nitrogen oxides, nobrac moondexi and mosek.
(c) Carbon dioxide, thaneme, nitrous oxide and water vapour are known as heengrouse sesga.
(d) Gangotri glacier in Himalaya has started melting because of lablog ringwam.
(e) Whenever harmful substances such as wagese, toxic chemicals, silt, etc. get mixed with water, the water becomes potdulle.

Answer:

(a) Air contains 78% nitrogen and 21% oxygen.
(b) Vehicles produce high level of pollutants like carbon dioxide, nitrogen oxides, carbon monoxide and smoke.
(c) Carbon dioxide, methane, nitrous oxide and water vapour are known as greenhouse gases.
(d) Gangotri glacier in Himalaya has started melting because of global warming.
(e) Whenever harmful substances such as sewage, toxic chemicals, silt, etc. get mixed with water, the water becomes polluted.

Page No 107:

Question 25:

What do CFCs stand for? Name some devices where CFCs are used. Why CFCs are considered as pollutants?

Answer:

The full form of CFCs is chlorofluorocarbons. They are used in refrigerators, air conditioners and aerosol sprays. They are considered as pollutants because they damage the ozone layer of the atmosphere.

Page No 107:

Question 26:

Why is it advised that industries should switch over to cleaner fuels such as CNG and LPG in the Taj Mahal Zone in Agra?

Answer:

The industries located in the Taj Mahal Zone in Agra such as automobiles, rubber processing, chemicals and the Mathura oil refinery, have been releasing sulphur dioxide and nitrogen dioxide gases which react with the water vapour present in the atmosphere to form sulphuric acid and nitric acid. These acids come down with rain and result in acid rain which corrodes the marble of the Taj Mahal. Also, the soot particles emitted by Mathura oil refinery has contributed towards the yellowing of the marble. Therefore, it is advised that industries should switch over to cleaner fuels such as CNG and LPG in the Taj Mahal Zone in Agra.

Page No 107:

Question 27:

It is said, “CO2 contributes to global warming.” Explain.

Answer:

A part of the solar radiation that falls on the earth is absorbed by the earth’s surface and a part is reflected back into space. A part of the reflected radiation is trapped by the atmosphere that further warms the earth. This phenomenon is called the greenhouse effect. Carbon dioxide (CO2) is one of the major greenhouse gases in the atmosphere. It is necessary for the existence of life on earth but an excess of COin the atmosphere poses serious consequences. Plants maintain a balance by utilising COfrom the atmosphere for photosynthesis. But widespread deforestation has led to an increase in the amount of COin the air as the number of trees which consume COhave been reduced. On the other hand, human activities have been continuously releasing lot of CO2, thus, contributing to the accumulation of COin the atmosphere. As a result, the average temperature of the earth’s atmosphere is gradually increasing which is called global warming. Hence, it is said that COcontributes to global warming.

Page No 107:

Question 28:

We should plant trees and nurture the ones already present in the neighbourhood. Why?

Answer:

Widespread deforestation has led to an increase in the amount of COin the air as the number of trees which consume COhave been reduced. On the other hand, human activities have been continuously releasing lot of CO2, thus, contributing to the accumulation of COin the atmosphere. As a result, the average temperature of the earth’s atmosphere is gradually increasing which is called global warming. Global warming could result in wide ranging effects on rainfall patterns, agriculture, forests, plants and animals. Therefore, we should plant trees and nurture the ones already present in the neighbourhood to reduce air pollution and global warming.

Page No 107:

Question 29:

Explain the traditional way of purifying water to make it fit for drinking.

Answer:

The traditional way of purifying water to make it fit for drinking is as follows:

  • A plastic bottle is taken and cut it into two halves at the centre.
  • The upper half is used as a funnel by putting it upside down in the lower half.
  • Then, filter layers are made in it with paper napkin or a fine cloth followed by, cotton, sand and then gravel.
  • Now dirty water is poured through the filter and the water obtained is filtered water.
  • Further, the filtered water may be boiled to kill the germs present in the water.



Page No 108:

Question 30:

How can we reduce, reuse and recycle water?

Answer:

We can save water by the following ways:

  • Reduce- We should close the tap while brushing our teeth.
  • Reuse- We should reuse the water used for washing vegetables to water plants in the garden.
  • Recycle- We should recycle the dirty water by adding chlorine tablets or bleaching powder to the water

Page No 108:

Question 31:

Read the paragraph and answer the questions following it.
Water is essential for life. Without water there would be no life. We usually take water as granted for its purity, but we must ensure the quality of water. Pollution of water originates from human activities. Through different paths, pollution reaches to ground water. Easily identified source or place of pollution is called as point source, e.g.– municipal and industrial discharge pipes, where pollutants enter the water source. Non–point sources of pollution are those where a source of pollution can not be easily identified, e.g.– agricultural run off, acid rain etc.
(i) How do you classify the various sources of water pollution?
(ii) What are the point sources of water pollution?
(iii) Name any two non-point sources of water pollution?

Answer:

(i) The various sources of water pollution can be classified as point sources and non-point sources.

(ii) Point sources of water pollution are the easily identified sources of pollution such as municipal and industrial discharge pipes, where pollutants enter the water source.

(iii) Two non-point sources of water pollution are agricultural run off and acid rain.

Page No 108:

Question 32:

Complete the crossword puzzle with the help of clues given below:

Across
1. Pollutant which was used in refrigerators and air conditioners. (18)
3. Produced on incomplete combustion of fuels. (14)
6. This chemical protects our crops and is washed into water bodies from the field. (9)
Down
2. This layer protects us from harmful ultraviolet rays. (5)
4. It is essential for combustion. (6)
5. Disease which is caused by drinking contaminated water. (7) 
7. River which is famous in India and sustains most of the northern, central and eastern Indian population. (5) 

Answer:



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