🌍 Pollution of Air and Water – MCQs for Class 8 Science

Part 1: Q1–Q25

Q1. Which of the following is a major cause of air pollution?

A) Burning of fuels
B) Photosynthesis
C) Boiling water
D) Breathing

✅ Correct Answer: A) Burning of fuels

Explanation:

• A) ✔ Burning coal, oil, petrol releases harmful gases like CO₂, CO, SO₂.
• B) Photosynthesis reduces CO₂, not pollution.
• C) Boiling water has negligible impact.
• D) Breathing is natural and does not cause pollution.

Q2. Which gas is the main contributor to the greenhouse effect?

A) Oxygen
B) Carbon dioxide
C) Nitrogen
D) Argon

✅ Correct Answer: B) Carbon dioxide

Explanation:

• B) ✔ CO₂ traps heat in the atmosphere, causing global warming.
• A, C, D) Do not significantly contribute to the greenhouse effect.

Q3. Which of the following is a primary pollutant?

A) Ozone
B) Sulphur dioxide
C) Smog
D) Peroxyacetyl nitrate

✅ Correct Answer: B) Sulphur dioxide

Explanation:

• B) ✔ SO₂ is directly released from industries and vehicles.
• A, C, D) Are secondary pollutants formed by chemical reactions in the atmosphere.

Q4. Acid rain is mainly caused by which gases?

A) CO₂ and O₂
B) SO₂ and NO₂
C) N₂ and H₂
D) H₂ and O₂

✅ Correct Answer: B) SO₂ and NO₂

Explanation:

• B) ✔ Sulphur dioxide and nitrogen oxides mix with rainwater to form acids.

Q5. Which of the following is the cleanest fuel?

A) Coal
B) Petrol
C) CNG
D) Diesel

✅ Correct Answer: C) CNG

Explanation:

• C) ✔ Compressed Natural Gas burns efficiently and produces fewer pollutants.
• A, B, D) Release more harmful gases and particulates.

Q6. Smog is a combination of:

A) Smoke and gas
B) Smoke and fog
C) Gas and dust
D) Dust and water

✅ Correct Answer: B) Smoke and fog

Explanation:

• B) ✔ Smog = smoke + fog, harmful to health.

Q7. Which of the following is NOT a water pollutant?

A) Industrial waste
B) Sewage
C) Plastic
D) Oxygen

✅ Correct Answer: D) Oxygen

Explanation:

• D) ✔ Oxygen is essential for aquatic life, not a pollutant.

Q8. Which gas is produced in large amounts during incomplete combustion of fuels?

A) Carbon monoxide
B) Carbon dioxide
C) Oxygen
D) Nitrogen

✅ Correct Answer: A) Carbon monoxide

Explanation:

• A) ✔ CO is poisonous and produced during incomplete combustion.

Q9. Which of these diseases is caused by drinking contaminated water?

A) Tuberculosis
B) Typhoid
C) Asthma
D) Diabetes

✅ Correct Answer: B) Typhoid

Explanation:

• B) ✔ Typhoid is waterborne, caused by Salmonella typhi.

Q10. Which layer of the atmosphere protects us from harmful UV rays?

A) Troposphere
B) Stratosphere
C) Ozone layer
D) Exosphere

✅ Correct Answer: C) Ozone layer

Explanation:

• C) ✔ Ozone absorbs UV radiation, preventing skin damage and cancer.

Q11. Which gas is mainly responsible for ozone layer depletion?

A) CO₂
B) CFCs
C) SO₂
D) NO₂

✅ Correct Answer: B) CFCs

Explanation:

• B) ✔ Chlorofluorocarbons (from refrigerators, sprays) break down ozone.

Q12. Which of the following is NOT an air pollutant?

A) Nitrogen
B) Carbon monoxide
C) Sulphur dioxide
D) Dust

✅ Correct Answer: A) Nitrogen

Explanation:

• A) ✔ Nitrogen is a natural, inert gas (78% of air).

Q13. Which water pollutant is most harmful for aquatic plants and animals?

A) Oxygen
B) Oil spill
C) Carbon dioxide
D) Nitrogen

✅ Correct Answer: B) Oil spill

Explanation:

• B) ✔ Oil blocks oxygen exchange, suffocating aquatic life.

Q14. The Taj Mahal is affected by:

A) Water pollution
B) Acid rain
C) Smog only
D) Noise pollution

✅ Correct Answer: B) Acid rain

Explanation:

• B) ✔ Acid rain (SO₂, NO₂) corrodes marble – “marble cancer.”

Q15. The main cause of water pollution in rivers is:

A) Rainwater
B) Industrial effluents and sewage
C) Aquatic plants
D) Rocks and soil

✅ Correct Answer: B) Industrial effluents and sewage

Explanation:

• B) ✔ Factories and untreated sewage are major river pollutants.

Q16. Which of these can reduce water pollution?

A) Using more plastic
B) Discharging untreated sewage
C) Treating wastewater before release
D) Overuse of pesticides

✅ Correct Answer: C) Treating wastewater before release

Explanation:

• C) ✔ Waste treatment removes harmful chemicals and pathogens.

Q17. Which harmful gas is released from burning plastic?

A) Oxygen
B) Carbon monoxide
C) Carbon dioxide
D) Dioxins

✅ Correct Answer: D) Dioxins

Explanation:

• D) ✔ Burning plastics releases dioxins, very toxic chemicals.

Q18. Which of these is NOT a renewable resource?

A) Solar energy
B) Wind energy
C) Coal
D) Water

✅ Correct Answer: C) Coal

Explanation:

• C) ✔ Coal is non-renewable and causes pollution when burnt.

Q19. Which of these practices reduces air pollution?

A) Using CNG vehicles
B) Burning leaves and garbage
C) Overusing fossil fuels
D) Cutting forests

✅ Correct Answer: A) Using CNG vehicles

Explanation:

• A) ✔ CNG vehicles emit fewer pollutants than petrol/diesel vehicles.

Q20. Which of these is a water purification method?

A) Filtration
B) Boiling
C) Chlorination
D) All of the above

✅ Correct Answer: D) All of the above

Explanation:

• D) ✔ Filtration, boiling, and chlorination kill germs and purify water.

Q21. Which gas is called a greenhouse gas?

A) Nitrogen
B) Oxygen
C) Carbon dioxide
D) Neon

✅ Correct Answer: C) Carbon dioxide

Explanation:

• C) ✔ CO₂ absorbs and re-emits heat → greenhouse effect.

Q22. Bhopal Gas Tragedy (1984) was caused by the leakage of:

A) Sulphur dioxide
B) Methyl isocyanate
C) Carbon monoxide
D) Nitrogen dioxide

✅ Correct Answer: B) Methyl isocyanate

Explanation:

• B) ✔ The MIC leak killed thousands and caused severe pollution.

Q23. Excess nitrogen compounds in water cause:

A) Eutrophication
B) Global warming
C) Ozone depletion
D) Acid rain

✅ Correct Answer: A) Eutrophication

Explanation:

• A) ✔ Nutrient enrichment → algal bloom → less oxygen → aquatic death.

Q24. The major cause of noise pollution in cities is:

A) Birds
B) Rainfall
C) Vehicles and industries
D) Thunderstorms

✅ Correct Answer: C) Vehicles and industries

Explanation:

• C) ✔ Honking, engines, and factory machinery cause noise pollution.

Q25. Which of these is an effect of acid rain?

A) Fertile soil formation
B) Increase in crop yield
C) Damage to buildings and plants
D) Increase in oxygen levels

✅ Correct Answer: C) Damage to buildings and plants

Explanation:

• C) ✔ Acid rain corrodes buildings, harms trees and aquatic life.

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