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Lakhmir Singh Solutions for Class 8 Science Chapter 18 Pollution of Air and Water - PDF

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Last updated date: 15th Apr 2024
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Lakhmir Singh For Class 8 Science Chapter 18 Pollution of Air and Water - Download Free PDF with Solution

Pollution is one of the gravest problems we are facing. It is destroying our planet in different ways. Several animal and plant species are on the verge of extinction due to pollution. To raise awareness, Class 8 Science Chapter 18 focuses on teaching what pollution is and its impact on the environment.


To understand the concepts and scientific principles of this chapter, refer to our Pollution of Air and Water Class 8 Lakhmir Singh Solutions and notes. These notes and solutions have been prepared by the subject experts of Vedantu to assist students in preparing this chapter.

Access Lakhmir Singh Solutions for Class 8 Science Chapter 18 Pollution of Air and Water

Very Short Answer Type Questions

1. Name the gas present in the atmosphere which is mainly responsible for causing global warming.

Ans: Carbon dioxide is the gas present in the atmosphere which is mainly responsible for causing global warming. It traps the heat of the sun in the earth’s atmosphere and prevents it from escaping back, which raises the temperature of the earth.


2. Name two gases present in the polluted air which can cause acid rain.

Ans: Sulphur dioxide and nitrogen oxides are the two gases present in polluted air which can cause acid rain. These gases get mixed with water vapours present in the atmosphere to form acids, which then dissolve in rainwater and fall on earth as acid rain.


3. Name all the major pollutants present in the air.

Ans: The major pollutants present in the air are; sulphur dioxide, nitrogen oxides, carbon monoxide, carbon dioxide, CFCs (Chlorofluorocarbons), SPM (Suspended particulate matter) like dust, smoke, and Fly ash.


4. Name the air pollutant that combines with the haemoglobin of our blood?

Ans: Carbon monoxide is an air pollutant that combines with the haemoglobin of our blood. It reduces the oxygen-carrying capacity of blood and can cause many respiratory problems.


5. Name the various air pollutants that are discharged by motor vehicle exhausts.

Ans: Sulphur dioxide, nitrogen oxides, carbon dioxide, carbon monoxide, and smoke are the various air pollutants discharged by motor vehicle exhaust. These pollutants not only pollute the air but also affect our health.


6. Which gas present in the upper atmosphere prevents ultraviolet radiations of the sun from reaching the earth?

Ans: Ozone gas in the upper atmosphere prevents ultraviolet radiations  of the sun from reaching the earth. Ozone gas is present as a layer around the earth's atmosphere called the ozone layer and protects us from harmful radiations of the sun.


7. Name any two diseases that are caused by drinking polluted water containing sewage.

Ans: Diseases like cholera, typhoid, diarrhoea, and jaundice are caused by drinking polluted water containing sewage as sewage contains many harmful microorganisms such as bacteria, fungi, viruses, etc.


8. Name any four toxic metals whose compounds are present in the industrial wastes.

Ans: Mercury, lead, arsenic, and nickel are examples of toxic metals whose compounds are present in industrial waste. This industrial waste when dumped in water bodies kills fish and other aquatic animals living in it.


9. What are the two types of chemicals used in agriculture which cause water pollution?

Ans: Fertilisers and pesticides are the chemicals used in agriculture that can cause water pollution. These chemicals get mixed with rain water and reach rivers, lakes, and ponds and pollute their water.


10. The use of excessive fertilisers in the fields leads to the deficiency of an important substance in the water of a nearby lake. Name that substance.

Ans: The use of excessive fertilisers in the fields leads to the deficiency of dissolved oxygen in the water of a nearby lake. This can result in the death of fish living in it due to oxygen starvation.


Short Answer Type Questions

11. What is the Ganga Action Plan? When was it launched and why?

Ans: Ganga Action Plan is an initiative taken to clean the polluted water of river Ganga and save it. It was launched in 1985 to reduce the pollution level in the water of the river Ganga.

Over the years the water of the river Ganga has been polluted to a great extent due to various uncontrolled human activities like dumping of garbage, untreated sewage, and toxic industrial waste into the river. Due to this, no aquatic life survives in it, making it an endangered river.  Therefore, the Ganga Action Plan was launched. 


12. Name any four pollutants which can cause water pollution. State any three ways by which water pollution can be controlled.

Ans: Water pollution is caused by dumping of the following into the water bodies:

  1. Untreated sewage from home

  2. Fertilisers

  3. Pesticides

  4. Untreated toxic industrial waste

Ways to control water pollution are:

  1. Treatment of sewage water before discharging it into the rivers.

  2. Minimising the use of fertilisers and pesticides.

  3. Treatment of the toxic waste produced by the industries before dumping it into rivers.


13. How do industries cause water pollution?

Ans: Industries like textile, leather, and oil refineries, etc., produce toxic chemicals as their waste product. These toxic chemicals are the compounds of harmful metals like mercury, lead, arsenic, etc. which can cause serious health issues.

This waste material is then discharged into the rivers without undergoing any treatment to make it harmless. This makes the river water polluted by toxic chemicals. This endangers aquatic life as well as poses a threat to human life too.


14. How can you help in reducing air pollution at the individual level?

Ans: Air pollution can be reduced at the individual level by adopting the following habits:

  1. We should not burn leaves, paper, and garbage in the open.

  2. We should grow more trees, which will help in controlling the level of carbon dioxide in the atmosphere.

  3. We should save electricity, which will reduce energy consumption and will result in less burning of coal, which is used to produce electricity.

  4. Furthermore, we should avoid burning crackers.


16. Explain the difference between the pure air and polluted air.

Ans: The difference between pure air and polluted air:


S. No. 

Pure air

Polluted air

1.

Pure air consists of a mixture of gases containing nitrogen, oxygen, carbon dioxide, argon, and a small amount of water vapours in it.

Polluted air consists of normal constituents of air along with the pollutants like sulphur dioxide, nitrogen oxides, carbon monoxide, smoke, etc.

2.

Pure air is clean and does not have any harmful effect on our health.

Polluted air can cause many health-related diseases.


17. What is the greenhouse effect? State its importance for us.

Ans: The warming up of the earth’s atmosphere due to the trapping of the sun’s heat by carbon dioxide present in the atmosphere is called the greenhouse effect. The gases which help in trapping the sun's heat rays are called greenhouse gases. These are carbon dioxide, methane, CFCs, etc.

The greenhouse effect is important for the existence of life on earth. Due to the greenhouse effect, the earth’s atmosphere is warm, which makes it habitable for all life forms. Without the greenhouse effect, the earth would have turned into a cold planet, and the survival of life would have been difficult.


18. Name two greenhouse gases? Which one of these produces the maximum greenhouse effect?

Ans: The greenhouse gases are carbon dioxide, methane, chlorofluorocarbons, etc. These are called greenhouse gases because they trap the heat of the sun’s rays in the earth's atmosphere and prevent it from escaping back. This makes the earth warm and habitable for many life forms

Out of all the gases, carbon dioxide is the one, which produces the maximum greenhouse effect and is responsible for warming up the earth’s atmosphere.


19. What depletes the ozone layer present in the atmosphere? What are the harmful effects of this depletion of the ozone layer on us?

Ans: The main reason for the depletion of the ozone layer is CFCs, i.e. chlorofluorocarbons. Chlorofluorocarbons make use in refrigerators, air conditioning, and aerosol sprays. CFCs react with the ozone layer present in the atmosphere and destroy it gradually.

The ozone layer helps to prevent the harmful ultraviolet rays of the sun from passing through the earth's atmosphere. Depletion of the ozone layer will allow the harmful UV rays to enter the earth and can cause skin cancer, cataract, and destruction of plants including crops.


20. Name one source and one harmful effect of the following air pollutants:

  1. Sulphur dioxide

Ans:  Sulphur dioxide is formed by burning of coal (in factories, thermal power plants) and by burning of petrol & diesel (in motor vehicles). It causes many respiratory problems including permanent lung damage and produces acid rain.


  1. Nitrogen oxides

Ans: It is produced by burning of petrol and diesel in motor vehicles and by burning coal in factories and thermal power plants. It attacks our breathing system and can lead to lung congestion. 


  1. Carbon monoxide

Ans: It is produced by incomplete combustion of fuels like wood, coal, kerosene, petrol, etc. in homes, factories, and motor vehicles. It combines with the haemoglobin in the blood and reduces its oxygen-carrying capacity.


  1. Chlorofluorocarbons (CFCs)

Ans: It is used in refrigerators, ACs, and aerosol sprays. It depletes the ozone layer because of which harmful UV rays reach the earth which can cause skin cancer, cataract, etc.


21. Explain why, even clear, transparent, and odourless water may not always be safe for drinking purposes.

Ans: Clear, transparent, and odourless water may not always be safe for drinking as it can have disease-causing microorganisms which are not visible to the naked eye. Drinking such water can cause the person to fall sick.

This can be avoided by purifying water by methods like filtration, boiling, and chlorination. This will get rid of the disease-causing microorganism and will make water fit for drinking.


22. Why hot water released by power plants and industries is considered a pollutant. Explain.

Ans: The hot water released by power plants and industries is  considered a pollutant because when such hot water is released into the river or lake, it increases the temperature of the river water or lake water. This increase in the temperature of the water affects the life of aquatic plants and animals living in rivers and lakes. They may not adapt to the rising temperature and can die.


23. Why does the increased level of nutrients, such as fertilisers, in the lake water affect the survival of aquatic organisms like fish?

Ans: When fertilisers are used in excess, they may flow with rainwater to rivers and lakes. Fertilisers are plant nutrients that are used for growth. Its increased amount in water causes rapid growth of algae over the entire surface of the water body. When these algae die, bacteria decompose them by using dissolved oxygen present in water. As a result, the amount of dissolved oxygen in water decreases too much and aquatic animals, like fish, die of oxygen starvation.


24. Explain how the use of pesticides in agriculture causes water pollution.

Ans: Pesticides are toxic chemicals used by farmers to protect their plants from pests and diseases. When they are used in excess, they can dissolve in rainwater and can reach water bodies.

Since pesticides are toxic in nature, their presence in water pollutes the water bodies and can cause the death of aquatic animals like fish. It can also enter the human body through the food chain and can affect our health.


25. Answer the following:

  1. Describe the threat to the Taj Mahal monument due to the pollution of air.

Ans: Due to air pollution, there is a high amount of air pollutants in the air. These air pollutants, especially sulphur dioxide and nitrogen oxides, get mixed with water vapours in the atmosphere to produce acid rain. This acid rain reacts with the carbonate of marble from which the Taj Mahal is made up of and corrodes it. Also, SPM present in the atmosphere discolours the white marble by turning it yellow.


  1. State any two ways to control air pollution.

Ans: Ways to control air pollution are:

  1. Making use of smokeless fuel like LPG, PNG, and biogas instead of wood, coal, and cow dung cakes.

  2. Making use of cleaner fuel like CNG in motor vehicles in place of petrol and diesel.


26. Answer the following:

  1. What is potable water? Name any two methods to make water safe for the purpose of drinking.

Ans: Potable water is that water that is fit for drinking. Water that is clear, transparent, and odourless is not always fit for drinking. It may contain harmful microorganisms which can make a person sick. So, it is necessary to make water safe  for drinking. This can be done by filtration, by using a porcelain filter or electric water filter, and by boiling water at 100⁰C. This will kill harmful microorganisms and will make water safe for drinking.


  1. State two ways in which one can conserve water at home by preventing its wastage.

Ans: Ways to conserve water at home are:

  1. Using water from washing rice, pulses, vegetables, etc. for watering plants at home.

  2. Use a bucket for bathing instead of bathing under running water.


Long Answer Type Questions

27. Answer the following:

  1. What is meant by water pollution? What are the different ways by which water gets polluted?

Ans: The contamination of the water of rivers, lakes, ponds, etc. by the addition of unwanted and harmful substances is called water pollution. This polluted water is unfit for consumption and cannot be used for drinking, cooking, bathing, etc. The unwanted and harmful substances added to water that makes it contaminated are called water pollutants.

Water gets polluted in different ways:

  1. When untreated sewage from homes is dumped into rivers.

  2. By excessive use of fertilisers in agriculture. It pollutes the water as well as decreases the dissolved oxygen present in it.

  3. By excessive use of pesticides.

  4. By discharging untreated toxic industrial waste into rivers.


  1. State the harmful effects of water pollution.

Ans: The harmful effects of water pollution are:

  1. Drinking water contaminated by untreated sewage causes many water-borne diseases like cholera, typhoid, jaundice, etc.

  2. Water contaminated by fertilisers can cause the death of fish due to oxygen starvation.

  3. Water, polluted with pesticides, can kill aquatic animals and can affect human health as these pesticides can enter the human body through the food chain.

  4. Water polluted by industrial waste is rich in toxic chemicals which can kill aquatic animals and can cause some serious illnesses in humans like blood poisoning, cancer, damage to the nervous system, etc.


28. Answer the following questions:

  1. What is air? Write the names of various constituents of the air.

Ans: Air is a mixture of gases and is present all around us. The main gases which constitute the air are nitrogen and oxygen, which are present in 78% and 21% by volume respectively. The other gases present in the air are carbon dioxide, argon, and water vapours. These are present in very small amounts in the air.

  • This air containing nitrogen, oxygen, carbon dioxide, argon, and water vapours is called pure air or clean air.

  • When along with the usual constituents, some pollutants like carbon monoxide, sulphur dioxide, smoke, dust, etc. are also present in the air, it is then, called polluted air. 


  1. What is air pollution?  What are the main sources of the pollution of air?

Ans: When  the air gets contaminated with harmful substances like sulphur dioxide, nitrogen oxides, carbon monoxide, smoke, dust, etc., then it is termed as air pollution. These substances that contaminate the air are called air pollutants. 

The main sources of air pollution are:

  1. Smokes emitted from homes by burning fuel like wood, cow dung cakes, kerosene, etc.

  2. Exhaust gases emitted by automobiles by burning petrol and diesel.

  3. Smoke emitted by factories, thermal power plants, oil refineries, metal industries, etc.

  4. Use of CFCs in refrigerators, ACs, and aerosol sprays cause air pollution

  5. Forest fires and volcanic eruptions also cause air pollution.


29. What is smog? How is it formed? What are its harmful effects?

Ans: Smog is a very deadly pollutant of air that is formed by the combination of smoke and fog. Both sulphur dioxide and nitrogen oxides contribute to the formation of smog.

Formation of smog:

  •  Both smoke and fog combine to form smog. 

  • Fog consists of minute water particles that are  suspended in air, near the surface of the earth during cold weather, and smoke consists of tiny carbon particles along with harmful gases like sulphur dioxide and nitrogen oxides.

  • When carbon particles, sulphur dioxide, and nitrogen oxides of smoke combine with condensed water vapour (i.e. fog) then smog is formed.

Harmful effects of smog:

  1. It causes cough and irritates the nose and eyes.

  2. It aggravates asthma and other lung diseases.

  3. It can also aggravate heart diseases.


30. What is acid rain? How is acid rain caused? Describe the harmful effects of acid rain.

Ans: Acid rain is rain that consists of  a small amount of acids like sulphuric acid and nitric acid formed from acidic gases like sulphur dioxide and nitrogen oxides, which are present in polluted air.

Cause of acid rain: 

  • The two main gases which cause acid rain are sulphur dioxide and nitrogen oxides. These are air pollutants produced by the burning of fossil fuels in factories, thermal power plants, etc. 

  • When sulphur dioxide and nitrogen oxides react with water vapours present in the air, they form sulphuric acid and nitric acid, respectively.

  • These acids combine with rain water and fall as acid rain on the earth.


Harmful effects of acid rain:

  1. Acid rain destroys forests by damaging the leaves of the forest trees. 

  2. It destroys the crops of farmers and makes the soil acidic, which is not ideal for the growth of crops.

  3. Acid rains kill aquatic animals like fish.

  4. Acid rain corrodes and damages statues, buildings, and historical monuments.


31. What is global warming? What are the harmful effects of the global warming?

Ans: The unusual rise in the temperature of the earth's atmosphere due to the excessive greenhouse effect caused by the increased amount of greenhouse gases like carbon dioxide in the atmosphere is called global warming.

Harmful effects of global warming are:

  1. It can cause an increase in the water level of the sea: 

  • With an increase in the temperature of the earth, the ice on the poles of the earth starts melting and the water level of the seas and oceans rises, which can cause flooding in low-lying areas. 

  • This results in damage to property and life


  1. It can reduce rainfall in certain areas:

This will lead to droughts in certain areas causing the death of plants and animals and can turn the area into a semi-desert.


  1. It poses a threat to the existence of life on earth:

The increase in the temperature of the earth, due to global warming, can cause intense heat waves and other consequences which can seriously affect life on earth.


Multiple Choice Questions (MCQs)

32. Which one of the following is not a greenhouse gas?

  1. Carbon dioxide

  2. Nitrous oxide

  3. Methane

  4. Nitrogen

Ans: The correct answer is d. nitrogen. Nitrogen is not a greenhouse gas. It is a constituent of pure air. Carbon dioxide, nitrous oxide, and methane are greenhouse gases, which can trap the heat of the sun’s rays.


33. Which one of the following air pollutants reduces the oxygen-carrying capacity of blood to a large extent?

  1. Carbon dioxide

  2. Nitrogen monoxide

  3. Carbon monoxide

  4. Sulphur dioxide

Ans: The correct answer is c. carbon monoxide. The carbon monoxide binds with the haemoglobin present in the blood and reduces the oxygen-carrying capacity of the blood. As a result, blood is not able to provide sufficient oxygen to the body parts.


34. The constituent of the polluted air which contributes to producing acid rain is:

  1. Nitrogen 

  2. Sulphur dioxide

  3. Oxygen

  4. Argon

Ans: The correct answer is b. sulphur dioxide. Sulphur dioxide gets mixed with water vapour present in the atmosphere to produce sulphuric acid, which then dissolves in rainwater. This rainwater then falls as acid rain.


35. The Kyoto Protocol is associated with one of the following. This one is:

  1. Reduction in the use of chlorofluorocarbons

  2. Reduction in the emission of greenhouse gases

  3. Reduction in the cutting of forest trees

  4. Reduction in pollution of freshwater sources

Ans: The correct answer is b. reduction in the emission of greenhouse gases. This will help in reducing global warming and will help us escape from its harmful effects. Many countries have signed this protocol to agree to reduce the emission of  greenhouse gases.


36. Which one of the following, will be reduced in the air in a city forest when a lot of dust and fly ash is emitted by a coal-based factory present in the vicinity?

  1. Nitrogen

  2. Carbon dioxide

  3. Oxygen

  4. Water vapour

Ans: The correct answer is c. oxygen. The burning of coal in factories results in the production of a lot of fly ash, smoke, carbon dioxide, etc. which results in an increasing amount of pollutants in surrounding areas. Also, due to fly ash and smoke the leaves of the forest trees can get covered by soot, preventing photosynthesis. This results in a decrease in the amount of oxygen.


37. Which one of the following diseases cannot be caused by drinking river water contaminated with untreated sewage?

  1. Cholera

  2. Typhoid

  3. Tuberculosis

  4. Diarrhoea

Ans: The correct answer is c. tuberculosis. Tuberculosis is an airborne disease that spreads by cough droplets. Cholera, typhoid, and diarrhoea are waterborne diseases caused by the contamination of drinking water with sewage.


38. Which one of the following statements about ozone is correct?

  1. It is essential for breathing

  2. It absorbs ultraviolet rays

  3. Its proportion in the air is about 3 percent.

  4. It is mainly responsible for global warming

Ans: The correct answer is b. It absorbs ultraviolet rays. The ozone layer protects the earth from the harmful effects of UV rays by not allowing them to enter the earth’s atmosphere.


39. Drinking water can be made absolutely safe by adding some of the:

  1. Aspirin tablets

  2. Iodine tablets

  3. Chlorine tablets

  4. Chlorophyll tablets

Ans: The correct answer is c. chlorine tablets. These tablets help disinfect drinking water by killing  bacteria and viruses present in it, and hence make water safe for consumption.


40. The excessive use of one of the following substances in agriculture can cause the death of fish in a pond by oxygen starvation. This substance is:

  1. Fertilisers

  2. Manures

  3. Pesticides

  4. Herbicides

Ans: The correct answer is a. fertilisers. When fertilisers get washed away to ponds, it results in the large-scale growth of algae in the water. When they are decomposed by bacteria, dissolved oxygen in the water gets reduced too much, which causes the death of fish by oxygen starvation.


41. Which one of the following is usually not a pollutant of water?

  1. Sewage 

  2. Fertiliser

  3. Fly ash

  4. Pesticide

Ans: The correct answer is c. fly ash. Fly ash is not a water pollutant. It is an air pollutant that is produced by the burning of coal in factories and thermal power plants.


42. Which of the following are used in electric water filters to kill all the harmful microorganisms present in the tap water and make it absolutely safe for drinking?

  1. Infrared radiation

  2. Gamma radiation

  3. Visible radiation

  4. Ultraviolet radiation

Ans: The correct answer is d. ultraviolet radiation. Ultraviolet radiation is used to kill all the harmful microorganisms and germs present in tap water. This makes the tap water safe for drinking.


43. Which one of the following is not an air pollutant?

  1. Sulphur dioxide

  2. Sewage

  3. CFCs

  4. SPM

Ans: The correct answer is b. sewage. Sewage is not an air pollutant. It is a water pollutant that contaminates the water bodies and makes its water unfit for consumption.


44. Which of the following air pollutants is capable of preventing photosynthesis in the plants?

  1. CFCs

  2. Nitrogen oxides

  3. Dust

  4. Carbon monoxide

Ans: The correct answer is c. dust. When leaves of trees and plants get covered in dust, the leaves are unable to perform photosynthesis as their pores get covered with dust particles. This prevents the exchange of gases and photosynthesis does not occur.


45. One of the following options does not contribute to producing acid rain. This one is

  1. Nitrogen dioxide

  2. Nitrogen monoxide

  3. Carbon monoxide

  4. Sulphur dioxide

Ans: The correct answer is c. carbon monoxide. Carbon monoxide does not create acid rain. Acid rain is produced by sulphur dioxide and oxides of nitrogen, i.e. nitrogen monoxide and nitrogen dioxide.


46. Which one of the following will reach the earth in greater amounts if the amount of chlorofluorocarbons released into the air increases?

  1. Infrared rays

  2. X-rays

  3. Gamma rays

  4. Ultraviolet rays

Ans: The correct answer is d. ultraviolet rays. If the amount of CFCs released into the air increases, the damage caused by CFCs to the ozone layer also increases. The ozone layer becomes thin and more UV rays enter the earth.


Questions Based on High Order Thinking Skills (HOTS)

47. The farmers use large amounts of substance P in the fields to increase the yield of crops. The excess of P gets dissolved in water and runs into a lake. The substance P causes rapid growth of the tiny green water plant Q in the lake, which covers the whole lake like a green sheet. When these plants Q die, the organisms, called R,  decompose them by utilising S dissolved in lake water. The amount of dissolved S in the water decreases too much, due to which the fish living in the lake suffocate and die. What are P, Q, R, and S?   

Ans:  P, Q, R, and S are as follows:

  • P which is used in large amounts by the farmer to increase the crop yield is fertiliser.   

  • Q which is a tiny green water plant whose growth increases because of fertiliser in water is algae.

  • R which decomposes algae are bacteria

  • S which bacteria use to decompose algae and whose amount dissolved in water decreases too much is oxygen.                                                                                                      


48. In many places the wastewater containing human excreta from homes is carried in big underground pipes and is dumped into a river which pollutes the river water.

  1. What is the common name given to such wastewater?

Ans: Such wastewater which consists of human excreta and is carried in big underground pipes is called sewage.


  1. Name five types of harmful organisms present in it.

Ans: The harmful organisms present in sewage are bacteria, protozoa, fungi, viruses, and parasites like worms.


  1. Name any five human diseases caused by drinking the river water contaminated with such wastewater.

Ans: Human diseases caused by drinking water contaminated with sewage are cholera, typhoid, diarrhoea, dysentery, and jaundice.


49. Match the statements given in column I with one or more statements given in column II:


Column I

Column II

(i) Prevents photosynthesis

(a) Sewage dumped in the river

(ii) Damage ozone layer

(b) Excess fertiliser in fields

(iii) Produce acid rain

(c) Carbon dioxide in the air

(iv) Kill fish by deoxygenating water

(d) Dust in the air

(v) Causes water-borne diseases

(e) CFCs

(vi) Leads to global warming

(f) Sulphur dioxide in air


Ans: The correct choices are:


Column I

Column II

(i) Prevents photosynthesis

(d) Dust in the air

(ii) Damage ozone layer

(e) CFCs

(iii) Produce acid rain

(f) Sulphur dioxide in the air

(iv) Kill fish by deoxygenating water

(b) Excess fertiliser in fields

(v) Causes water-borne diseases

(a) Sewage dumped in the river 

(vi) Leads to global warming

(c) Carbon dioxide in air


50. State one way in which the air pollution caused by the burning of fossil fuels in transport and industries can kill fish living in the same lake.

Ans. Air pollution caused by the burning of fossil fuels in transport and industry can kill fish living in the same lake because of the acid rain.

  • Burning of fossil fuels results in the release of sulphur dioxide and nitrogen oxides, which in the atmosphere combine with water vapours to form acids. These acids then get dissolved in rainwater and fall as acid rain.

  • This acid rain, when it falls in lakes, turns the water of the lake acidic and makes it unsuitable for the survival of aquatic life. As a result of which, aquatic animals like fish die.


51. The incomplete combustion of firewood in homes produces a very poisonous gas named X. When inhaled, gas X combines with the substance Y present in the blood and reduces the capacity of blood to carry gas Z causing many respiratory problems and suffocation. What are X, Y, and Z? 

Ans: X, Y, Z are as follows:

  • X which is a poisonous gas formed by incomplete combustion of firewood is carbon monoxide.

  • Y with which carbon monoxide combines in blood, is haemoglobin

  • Z is oxygen. Carbon monoxide combines with haemoglobin in blood to reduce the oxygen-carrying capacity of the blood.


Importance of Lakhmir Singh Class 8 Science Chapter 18 Pollution of Air and Water

As mentioned earlier, this chapter holds immense importance as it teaches about air and water pollution. Air and water are the two prime factors that sustain life on this planet. We are destroying these resources at a threatening speed.


This chapter explains pollution and how it is created by manmade sources. It also explains the different natural sources of air and water pollution. It defines and explains different types of pollution with examples.


Progressing further, this chapter explains how crucial water and air are for the survival of all the organisms on earth. It explains how air pollution is dangerous and causes various diseases. Students will find out the natural and manmade sources of air pollution. They will also understand the impact of modern civilisation on air pollution.


This chapter will also describe what air pollutants are. To understand them properly, refer to the Chapter 18 Class 8 Science Lakhmir Singh Solutions and get specific answers. Find out how these pollutants are produced and cause harm to our atmosphere.


In this chapter, students will also find the causes and impact of global warming. They will learn elaborately about greenhouse gases and the greenhouse effect. Hence, this chapter is crucial to learning about pollution and its impact on the environment.


Benefits of Class 8 Science Chapter 18 Pollution of Air and Water Solutions PDF

  • These solutions have been framed by following the latest syllabus to offer accurate answers to all exercise questions. By following these solutions, students will find the answers to questions like how does air gets polluted Class 8 Chapter 18 solution.

  • Students will also be able to find out the difference between air pollution and water pollution Class 8 and other fundamental topics. It will make their preparation for this chapter better.

  • Resolving doubts will not be a problem anymore. You can refer to the solutions anytime according to your study schedules. Add more convenience to your study and stay ahead of the competition.

  • Find the best answering formats suggested by the experts in these solutions to enhance your answering skills.


Download Pollution of Air and Water Class 8 solutions PDF

Get the free PDF version of the notes and solutions for this chapter. Complete the study material you have collected for this crucial part of the Class 8 Science syllabus. Make sure you have the right material to prepare and score more in the exams without hassle.

FAQs on Lakhmir Singh Solutions for Class 8 Science Chapter 18 Pollution of Air and Water - PDF

1. What is global warming?

The gradual increase in the average temperature of the earth due to the accumulation of greenhouse gases is called global warming.

2. What are CFCs?

CFCs are chemical compounds. CFC is the short form for chlorofluorocarbons, a family of gases that harm the ozone layers.

3. What are the causes of water pollution?

The major causes of water pollution are industries, urbanisation, unsafe religious practices, social practices, and agriculture.

4. What is potable water?

The water that is suitable for drinking is called potable water. Municipal corporations supply it to the cities.

5. How can we make water drinkable?

By boiling water, filtering, and chlorinating, we can make water drinkable. These processes remove pollutants and germs from the water.