Pollution of Air and Water – Short Answer Type Questions
Class 8
Science
NCERT – Chapter 18
Strictly Based on NCERT Syllabus
CBSE Class 8 Science – Chapter 18: Pollution of Air and Water
Topic-wise Short Answer Type Questions with clear NCERT-based solutions for strong exam preparation.
Useful For: Class Tests • Periodic Assessments • Half-Yearly & Annual Exams • CBSE Class 8 Board Exam Standard Preparation
This set of Short Answer Type Questions is a part of
CBSE Class 8 Science – Chapter Wise Study Materials Based on NCERT.
All questions are framed strictly from the NCERT textbook for
Chapter 18: Pollution of Air and Water and provide clear, easy-to-understand answers
ideal for CBSE Class 8 board exams standard revision.
Short Answer Type Questions – Topic-wise
Topic 1: Basics of Pollution and Environment
Questions 1–7
Q1. Define pollution and give one example each of natural and man-made pollution.
Ans: Pollution is any undesirable change in the physical, chemical or biological characteristics of the environment that harms living beings.
A volcanic eruption is an example of natural pollution, while smoke from vehicles is an example of man-made pollution.
Q2. What is a pollutant? Name any four common pollutants.
Ans: Any substance which causes pollution is called a pollutant.
Four common pollutants are carbon monoxide, sulphur dioxide, sewage and plastic waste.
Q3. How do human activities disturb the natural balance of air and water?
Ans: Human activities such as burning fossil fuels, cutting trees, releasing untreated sewage and industrial effluents add harmful substances to air and water.
These activities change their natural composition and make them unfit for healthy life.
Q4. Why are we more concerned about pollution in big cities?
Ans: Big cities have heavy traffic, many industries and dense population.
More vehicles and factories release large amounts of smoke and waste, and the higher population produces more sewage and garbage, leading to greater pollution.
Q5. Differentiate between biodegradable and non-biodegradable pollutants with one example of each.
Ans: Biodegradable pollutants can be broken down by microorganisms, e.g., vegetable waste.
Non-biodegradable pollutants cannot be easily decomposed, e.g., plastic bags and synthetic detergents.
Q6. State any two harmful effects of pollution on human health.
Ans: Pollution can cause respiratory diseases like asthma and bronchitis, and may lead to eye irritation, skin allergies, and water-borne diseases such as cholera.
Q7. Why is it important to keep the environment pollution free?
Ans: A pollution-free environment ensures clean air, safe water and healthy soil.
It supports good health, better crop yield, survival of other living organisms and maintains ecological balance.
Topic 2: Air Pollution – Causes, Pollutants and Effects
Questions 8–17
Q8. What is air pollution? Name two gases that cause air pollution.
Ans: Air pollution is the presence of harmful and unwanted substances in the air that make it unfit for living beings.
Gases such as sulphur dioxide (SO₂) and nitrogen oxides (NOx) cause air pollution.
Q9. How does incomplete combustion of fuels affect air quality?
Ans: Incomplete combustion of fuels produces carbon monoxide, a poisonous gas.
When inhaled, it reduces the oxygen-carrying capacity of blood, causing breathing difficulties and damage to the heart and brain.
Q10. Mention any three sources of air pollution.
Ans: Three sources of air pollution are:
(i) Vehicle exhaust, (ii) Smoke from factories and power plants, (iii) Burning of garbage, crop residues and firewood.
Q11. What is Suspended Particulate Matter (SPM)? Why is it harmful?
Ans: Suspended Particulate Matter is a mixture of tiny solid or liquid particles like dust, smoke, soot and ash present in air.
When inhaled, SPM can irritate the nose and lungs and can cause respiratory problems.
Q12. How does air pollution affect plants?
Ans: Air pollution can damage leaves, reduce photosynthesis and slow down plant growth.
Acidic pollutants can burn leaf surfaces and lead to early leaf fall and lower crop yield.
Q13. What is carbon monoxide? Why is it dangerous for human beings?
Ans: Carbon monoxide is a colourless and odourless gas produced by incomplete burning of fuels.
It combines with haemoglobin to form carboxyhaemoglobin, which prevents blood from carrying enough oxygen, leading to suffocation and even death.
Q14. Explain how deforestation can indirectly increase air pollution.
Ans: Trees absorb carbon dioxide and release oxygen.
When forests are cut, fewer trees are left to absorb CO₂, so its amount increases in air.
This contributes to global warming and indirectly worsens air pollution.
Q15. Why are children and elderly people more affected by air pollution?
Ans: Children and elderly people have weaker immune systems and more sensitive lungs.
Polluted air can easily cause breathing problems, allergies and infections in them compared to healthy adults.
Q16. What do you understand by the term “air quality”?
Ans: Air quality refers to how clean or polluted the air is.
It is judged by measuring the concentration of pollutants in air and is often represented by the Air Quality Index (AQI).
Q17. Name two respiratory diseases caused or aggravated by air pollution.
Ans: Asthma and bronchitis are two respiratory diseases that can be caused or worsened by air pollution.
Topic 3: Smog, Acid Rain, Greenhouse Effect and Ozone Layer
Questions 18–24
Q18. What is smog? Write one harmful effect of smog.
Ans: Smog is a thick, fog-like layer formed when smoke or pollutants mix with fog near the ground.
It reduces visibility and can cause irritation in eyes and breathing problems.
Q19. How is acid rain formed?
Ans: Gases like sulphur dioxide and nitrogen oxides released from factories and vehicles dissolve in rainwater to form sulphuric and nitric acids.
When this acidic rain falls on the Earth, it is known as acid rain.
Q20. Mention any two harmful effects of acid rain.
Ans: Acid rain damages buildings and monuments made of marble, corrodes metals and harms plant leaves.
It can also make water bodies acidic and affect aquatic life.
Q21. What is the greenhouse effect?
Ans: The greenhouse effect is the process by which greenhouse gases like carbon dioxide and methane trap heat in the Earth's atmosphere,
keeping the planet warm enough to support life.
Q22. How does global warming affect the Earth?
Ans: Global warming leads to the melting of glaciers and polar ice caps, causing a rise in sea level.
It can result in flooding of coastal areas, changes in rainfall patterns and more frequent extreme weather events.
Q23. What is the role of the ozone layer in the atmosphere?
Ans: The ozone layer acts like a protective shield in the stratosphere.
It absorbs most of the harmful ultraviolet (UV) radiation from the Sun, preventing it from reaching the Earth's surface and protecting living beings.
Q24. How do chlorofluorocarbons (CFCs) harm the ozone layer?
Ans: CFCs released from old refrigerators, air-conditioners and aerosol sprays reach the upper atmosphere.
There they break down and release chlorine atoms, which destroy ozone molecules, leading to thinning of the ozone layer.
Topic 4: Control and Prevention of Air Pollution
Questions 25–30
Q25. Explain any three ways to reduce air pollution caused by vehicles.
Ans: (i) Use public transport, carpooling, walking or cycling instead of personal vehicles.
(ii) Use cleaner fuels like CNG, LPG and electricity.
(iii) Get vehicles regularly serviced to ensure complete combustion of fuel.
Q26. How do trees help in improving air quality?
Ans: Trees absorb carbon dioxide and release oxygen during photosynthesis, which improves air quality.
Their leaves also trap dust and particulate matter, thereby reducing pollution levels.
Q27. Why should garbage and dry leaves not be burnt in the open?
Ans: Burning garbage and dry leaves produces a lot of smoke and harmful gases such as carbon monoxide.
This increases air pollution and can cause breathing problems and irritation in eyes.
Q28. What is the role of factory chimneys with filters in controlling air pollution?
Ans: Factory chimneys fitted with filters or electrostatic precipitators trap harmful particles like ash and soot.
As a result, cleaner gases are released into the atmosphere, reducing air pollution.
Q29. What is Air Quality Index (AQI)? How is it useful?
Ans: Air Quality Index is a number and colour code that indicates how clean or polluted the air is in a particular area.
It helps people know whether the air is safe to breathe and take precautions on highly polluted days.
Q30. How can you, as a student, help in controlling air pollution?
Ans: I can use a bicycle or walk for short distances, plant and care for trees, avoid bursting too many firecrackers,
and spread awareness among family and friends about the importance of clean air.
Topic 5: Water Pollution – Causes, Effects and Eutrophication
Questions 31–38
Q31. Define water pollution and give two examples of pollutants that cause it.
Ans: Water pollution is the contamination of water bodies such as rivers, lakes and seas by harmful substances, making the water unfit for use.
Sewage and chemical effluents from factories are two major water pollutants.
Q32. How does domestic sewage pollute water bodies?
Ans: Domestic sewage contains soaps, detergents, food waste, oils and human excreta.
When discharged into water bodies without treatment, it reduces dissolved oxygen and introduces harmful germs, polluting the water.
Q33. Explain how agricultural activities lead to water pollution.
Ans: Excess fertilisers and pesticides sprayed on fields are washed away by rainwater into nearby ponds and rivers.
These chemicals mix with water, harm aquatic life and make the water unsafe for drinking.
Q34. What are industrial effluents? How do they affect aquatic life?
Ans: Industrial effluents are liquid wastes released by factories, often containing acids, heavy metals, dyes and toxic chemicals.
When released into water bodies, they poison fish and other aquatic organisms and may cause bioaccumulation.
Q35. What is eutrophication? Briefly describe its harmful effect.
Ans: Eutrophication is the enrichment of water bodies with nutrients like nitrates and phosphates from fertilisers and sewage.
It causes excessive growth of algae, which on decomposing consume dissolved oxygen, leading to the death of fish and other aquatic animals.
Q36. How does water pollution affect human health?
Ans: Polluted water may contain disease-causing germs and toxic chemicals.
Drinking such water can cause diseases like cholera, typhoid, diarrhoea and may also damage organs like the liver and kidneys.
Q37. Why is it harmful to throw plastic bags and religious waste into rivers?
Ans: Plastic bags do not decompose and choke the flow of water.
Religious waste, if wrapped in plastic, decays and releases foul smell and germs.
Together they degrade water quality and harm aquatic organisms.
Q38. State any three measures to reduce water pollution in rivers.
Ans: (i) Treat sewage and industrial effluents before releasing them into rivers.
(ii) Avoid throwing garbage, plastics and religious materials into water.
(iii) Use fertilisers and pesticides in limited amounts and promote organic farming.
Topic 6: Potable Water and Purification Methods
Questions 39–44
Q39. What is potable water? Mention two qualities of potable water.
Ans: Potable water is water that is safe for drinking.
It should be free from harmful germs and toxic chemicals and should be clear, with a pleasant taste and odour.
Q40. How does boiling make water safe for drinking?
Ans: Boiling water for about 10–15 minutes kills most of the disease-causing microorganisms present in it.
Thus, it is a simple and effective method to make water safer for drinking at home.
Q41. Explain how chlorination is used to disinfect drinking water.
Ans: In chlorination, a calculated amount of chlorine or bleaching powder is added to water.
Chlorine kills harmful bacteria and other germs present in the water, making it fit for drinking.
Q42. How do modern water purifiers clean water?
Ans: Modern water purifiers use filters to remove suspended impurities and technologies like UV treatment and Reverse Osmosis (RO)
to kill germs and remove dissolved salts and chemicals, providing clean drinking water.
Q43. Why should we not waste clean drinking water?
Ans: Clean drinking water is limited and many people still do not have access to it.
Wasting potable water can lead to shortages in future, so it must be used carefully and conserved.
Q44. Suggest two simple methods to purify muddy water before boiling.
Ans: Muddy water can be allowed to settle so that heavier particles sink at the bottom and clear water is decanted.
It can also be filtered through a clean cloth or household filter before boiling.
Topic 7: Sewage Treatment, Wastewater Management and Public Role
Questions 45–50
Q45. What is sewage? List its main components.
Ans: Sewage is wastewater from homes, offices, hospitals and industries.
It mainly contains human excreta, food waste, soaps, detergents, oils and other dissolved and suspended impurities.
Q46. Why is it necessary to treat sewage before discharging it into water bodies?
Ans: Untreated sewage contains harmful germs and organic waste.
If released directly into water bodies, it spreads diseases, reduces dissolved oxygen and kills aquatic life.
Therefore, sewage must be treated to remove pollutants.
Q47. Briefly describe the primary treatment of sewage.
Ans: In primary treatment, sewage is passed through screens to remove large objects like rags and plastics.
Then it is allowed to stand in large tanks so that heavy solids settle at the bottom and lighter materials like oil float on top and are removed.
Q48. What happens during the secondary treatment of sewage?
Ans: During secondary treatment, air is pumped into sewage in aeration tanks.
Useful microorganisms grow and break down organic matter.
The mixture is then allowed to settle, forming sludge, and the clearer water is disinfected before discharge.
Q49. Suggest three ways in which you can help reduce water pollution in daily life.
Ans: (i) Avoid throwing oils, paints or medicines into drains.
(ii) Do not waste water and close taps properly.
(iii) Dispose of household garbage properly instead of dumping it near water bodies.
Q50. Why is public awareness important in controlling pollution of air and water?
Ans: Laws and technology alone cannot control pollution unless people understand its harmful effects.
Public awareness encourages citizens to change their habits, follow rules, save resources and actively participate in keeping the environment clean.