Pollution of Air and Water – MCQs with Answers and Explanations
Class 8
Science
NCERT – Chapter 18
Strictly Based on NCERT Syllabus
CBSE Class 8 Science – Chapter 18: Pollution of Air and Water
Topic-wise Multiple Choice Questions (MCQs) with answers and explanations for strong NCERT-based practice.
Useful For: Class Tests • Periodic Assessments • Half-Yearly & Annual Exams • CBSE Class 8 Board Exam Standard Preparation
This page provides 50 Multiple Choice Questions (MCQs) from
Chapter 18: Pollution of Air and Water, organised topic-wise as part of the
CBSE Class 8 Science – Chapter Wise Study Materials Based on NCERT.
Each MCQ comes with the correct answer and a clear, concept-building explanation,
strictly aligned with the NCERT textbook and ideal for CBSE Class 8 board exams standard preparation.
MCQs – Topic-wise Practice for Chapter 18: Pollution of Air and Water
Topic 1: Basics of Pollution and Environment
MCQs 1–8
Q1. Pollution is best defined as:
Answer: C
Pollution means any undesirable change in the physical, chemical or biological characteristics
of the environment that adversely affects living organisms. So option C is correct.
Q2. Any substance that causes pollution is called a:
Answer: B
A substance which, when present in greater than normal amount, causes pollution is called a
pollutant. The term “pollutant” is directly used in the NCERT definition.
Q3. Which of the following is NOT a form of pollution studied in this chapter?
Answer: B
Chapter 18 mainly deals with air and water pollution. Noise pollution is important
but is not a focus of this particular NCERT chapter.
Q4. The surroundings which include air, water, soil, plants and animals are together called:
Answer: C
The term environment is used for everything that surrounds us,
including air, water, soil and living organisms. Hence, option C is correct.
Q5. Which of the following is a natural cause of pollution?
Answer: B
Volcanic eruptions release gases and ash naturally, causing pollution.
Other options are man-made sources of pollution.
Q6. Which of these combinations shows only human activities causing pollution?
Answer: C
Burning fuels, dumping sewage and cutting trees are all human (anthropogenic) activities
that increase pollution, so option C is correct.
Q7. Which of the following can be both an air and water pollutant?
Answer: A
Sulphur dioxide mainly pollutes air, but when it dissolves in rainwater it forms acid rain,
which pollutes water too. Thus it can affect both air and water.
Q8. A pollutant that can be broken down by natural processes is called:
Answer: B
Biodegradable pollutants are decomposed by microorganisms.
Non-biodegradable pollutants like plastics persist for a long time.
Topic 2: Air Pollutants and Their Sources
MCQs 9–18
Q9. Air pollution is caused when:
Answer: C
Air becomes polluted when harmful substances (pollutants) are present beyond safe limits.
So option C matches the definition of air pollution.
Q10. Which gas is produced by incomplete combustion of fuels?
Answer: B
Incomplete combustion of fuels produces carbon monoxide (CO), a poisonous gas,
whereas complete combustion forms carbon dioxide (CO₂).
Q11. Which of these is NOT a major source of air pollution?
Answer: C
Sewage treatment plants mainly treat wastewater. They are not a major source of air pollution,
while the others emit smoke and gases.
Q12. The major component of air is:
Answer: C
Air is mainly composed of about 78% nitrogen and 21% oxygen.
Nitrogen is therefore the major component by volume.
Q13. Suspended Particulate Matter (SPM) consists of:
Answer: B
SPM includes tiny solid or liquid particles like dust, soot, smoke droplets that remain suspended in air and pollute it.
Q14. Which of these is a greenhouse gas?
Answer: C
Carbon dioxide is a major greenhouse gas. It traps heat in the atmosphere, contributing to the greenhouse effect and global warming.
Q15. Which fuel is known as a clean fuel for vehicles?
Answer: B
Compressed Natural Gas (CNG) produces less smoke and fewer harmful gases.
Hence it is called a clean fuel, as mentioned in NCERT for Delhi buses.
Q16. Which pollutant is mainly responsible for respiratory problems like asthma?
Answer: B
Gases like sulphur dioxide and particulate matter (dust, smoke) irritate the respiratory tract and can trigger asthma and bronchitis.
Q17. Major air pollutants from vehicle exhausts are:
Answer: A
Vehicle exhaust contains carbon monoxide (CO), nitrogen oxides (NOx) and unburnt hydrocarbons, which are harmful pollutants.
Q18. The main greenhouse gas produced by burning fossil fuels is:
Answer: B
Burning coal, petrol and diesel mainly produces carbon dioxide,
which is the most important human-made greenhouse gas.
Topic 3: Smog, Acid Rain, Global Warming and Ozone
MCQs 19–26
Q19. Smog is a combination of:
Answer: A
The word smog itself comes from “smoke” + “fog” and is a smoky, polluted fog seen in big cities, especially in winter.
Q20. Acid rain is mainly caused by which gases?
Answer: B
Sulphur dioxide (SO₂) and nitrogen oxides (NOx) dissolve in rainwater to form acids, causing acid rain which damages plants and buildings.
Q21. Global warming refers to:
Answer: A
Global warming is the gradual rise in the average temperature of the whole Earth due to enhanced greenhouse effect.
Q22. Which of the following is a harmful effect of global warming?
Answer: A
One major effect of global warming is melting of glaciers and polar ice, leading to a rise in sea level and flooding of coastal areas.
Q23. The ozone layer protects us from:
Answer: C
The ozone layer in the stratosphere absorbs most of the ultraviolet (UV) rays from the Sun, protecting life on Earth from their harmful effects.
Q24. Ozone layer is present in which part of the atmosphere?
Answer: B
The protective ozone layer lies in the stratosphere, above the troposphere where weather occurs.
Q25. Which chemicals are mainly responsible for the depletion of the ozone layer?
Answer: A
Chlorofluorocarbons (CFCs), used earlier in refrigerators and aerosol sprays, break down ozone molecules and cause thinning of the ozone layer.
Q26. Which of the following is NOT an effect of acid rain?
Answer: B
Acid rain actually reduces soil fertility by harming soil organisms and nutrients.
So “increased fertility” is incorrect and hence the right answer here.
Topic 4: Control and Prevention of Air Pollution
MCQs 27–34
Q27. Which of the following helps reduce air pollution from vehicles?
Answer: B
Using public transport and carpooling reduces the number of vehicles on roads, lowering overall fuel consumption and pollution.
Q28. Planting trees helps in controlling air pollution because trees:
Answer: B
Trees take in CO₂ and give out O₂ during photosynthesis, and their leaves also trap dust, thus improving air quality.
Q29. Chimneys of some factories have filters fitted in them to:
Answer: B
Filters or electrostatic precipitators in chimneys trap dust and ash so that cleaner gases are released into the atmosphere.
Q30. Which of the following activities will NOT help in reducing air pollution?
Answer: B
Burning leaves and garbage releases smoke and harmful gases, so it increases air pollution instead of reducing it.
Q31. The Air (Prevention and Control of Pollution) Act in India was passed to:
Answer: B
This Act aims to prevent and control air pollution by setting standards and empowering authorities to take action against polluters.
Q32. The Air Quality Index (AQI) is used to:
Answer: C
AQI is a number and colour code that tells us about the quality of air in a particular area and its impact on health.
Q33. Which of the following is an individual-level step to reduce air pollution?
Answer: B
Using a bicycle or walking for short distances saves fuel and produces zero emissions, directly reducing air pollution.
Q34. Why should we not burn firecrackers in large numbers?
Answer: C
Firecrackers release a lot of smoke, particulate matter and toxic gases, which greatly increase air pollution in a short time.
Topic 5: Water Pollution and Eutrophication
MCQs 35–43
Q35. Water pollution is:
Answer: B
Water pollution occurs when harmful substances (pollutants) enter water bodies and make the water unfit for use and harmful to aquatic life.
Q36. Which of the following is a major source of water pollution in cities?
Answer: B
Untreated sewage from homes and markets is often discharged into rivers and lakes, causing serious water pollution in cities and towns.
Q37. Which of these can be present in domestic sewage?
Answer: D
Domestic sewage contains a mixture of soaps, detergents, food particles, oils and human excreta, all of which pollute water if not treated properly.
Q38. The enrichment of water bodies with nutrients leading to excessive growth of algae is called:
Answer: B
When fertilisers and sewage add nutrients to water, it leads to eutrophication, causing algal blooms and harm to aquatic life.
Q39. The thick green layer formed on the surface of a polluted pond is mainly due to:
Answer: B
Excess nutrients cause rapid growth of algae, forming a green scum called an algal bloom on the surface of water bodies.
Q40. Which of the following is NOT a water-borne disease?
Answer: C
Asthma is related to the respiratory system and air pollution, whereas cholera, typhoid and diarrhoea can spread through polluted water.
Q41. Industrial effluents are:
Answer: B
Industrial effluents are liquid wastes released by industries, often containing harmful chemicals, dyes and heavy metals that pollute water bodies.
Q42. How does water pollution affect aquatic animals like fish?
Answer: B
Decomposition of organic pollutants uses up dissolved oxygen. Low oxygen levels cause fish and other aquatic animals to suffocate and die.
Q43. Which action will help in reducing water pollution in rivers?
Answer: B
Using fewer chemical fertilisers and pesticides reduces the amount of harmful chemicals washed into rivers, thus helping to reduce water pollution.
Topic 6: Potable Water and Purification Methods
MCQs 44–47
Q44. Potable water is:
Answer: B
Potable water is defined as water which is fit and safe for human consumption (drinking), with no harmful germs or toxic chemicals.
Q45. Which method is most commonly used at home to kill germs in water?
Answer: B
Boiling water for sufficient time kills most disease-causing microorganisms and is a simple, commonly used method at home.
Q46. Chlorine is added to drinking water to:
Answer: C
Chlorination is the process of adding chlorine to water to disinfect it by killing harmful microorganisms.
Q47. RO in water purifiers stands for:
Answer: A
RO stands for Reverse Osmosis, a process used in modern purifiers to remove dissolved impurities and make water safer to drink.
Topic 7: Sewage, Treatment and Public Role
MCQs 48–50
Q48. Sewage is:
Answer: C
Sewage is wastewater from homes, offices and other buildings that contains human excreta, food waste, soaps and many other impurities.
Q49. In a sewage treatment plant, air is bubbled through the sewage to:
Answer: B
In the aeration tank, air is pumped to provide oxygen so that microorganisms can grow and decompose the organic matter present in sewage effectively.
Q50. Which of the following actions by citizens helps reduce pollution of air and water?
Answer: C
Using public transport reduces vehicle pollution, and proper waste disposal prevents garbage from entering water bodies,
so option C supports both air and water pollution control.