CAPF AC 2023 Q30: Environment & Ecology – Pollution & Waste Management
- (a) The Sun causes heating of upper layer of atmosphere.
- (b) The burning of fossil fuels releases oxides of carbon, nitrogen and sulphur in the atmosphere.
- (c) The electrical charges are produced due to friction amongst clouds.
- (d) The atmosphere of the Earth contains acids.
Answer: (b) The burning of fossil fuels releases oxides of carbon, nitrogen and sulphur in the atmosphere.
Explanation
Cause of acid rain
How to think: rain turns acidic when acid-forming gases dissolve in it.
These gases come mainly from burning coal and petroleum in power plants, factories and vehicles.
| Gas | Source | Acid formed in rain |
|---|---|---|
| Sulphur dioxide | Coal-fired power plants, smelters | Sulphuric acid |
| Nitrogen oxides | Vehicles, power plants | Nitric acid |
| Carbon dioxide | All burning | Weak carbonic acid |
How acidic: normal rain has a pH of about 5.6 because of carbon dioxide.
Rain with a pH below 5.6 is called acid rain.
Damage: it harms forests, lakes, soil and buildings.
The yellowing of the Taj Mahal marble is linked to it (marble cancer).
Answer: (b).
Why each option is right or wrong
- (a) Incorrect. Heating of the upper atmosphere by the Sun does not make rain acidic.
- (b) CORRECT. Burning fossil fuels releases oxides of sulphur and nitrogen that form acids.
- (c) Incorrect. Friction among clouds causes lightning, not acid rain.
- (d) Incorrect. The atmosphere does not naturally hold acids in such amounts.
Key point
Acid rain: pH below 5.6; sulphur dioxide and nitrogen oxides from fossil fuels form sulphuric and nitric acids. Effects: marble cancer (Taj Mahal, Mathura refinery), dead lakes, damaged forests. Control: flue gas desulphurisation, cleaner fuels.
Remember
Acid rain: SO₂ and NOx from fossil fuels; pH below 5.6.
Common mistakes
- Blaming carbon dioxide alone; the main culprits are sulphur and nitrogen oxides.
- Thinking normal rain is perfectly neutral at pH 7.
- Linking acid rain with ozone depletion, a separate problem.
Exam tip
Educated guess: acid rain is a pollution problem of industrial regions. Only one option mentions a human source of pollution.
Sources
- NCERT Class XI Chemistry — Environmental Chemistry (acid rain)
- NCERT Class VIII Science — Pollution of Air and Water (case study: the Taj Mahal)