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UPSC Prelims 1988 · Environment · Pollution Files
Acid rain is caused by pollution of environment by
- (a) Carbon dioxide and nitrogen
- (b) Carbon monoxide and carbon dioxide
- (c) Ozone and carbon dioxide
- (d) Nitrous oxide and Sulphur dioxide
Show the answer and explanation
Answer: (d) Nitrous oxide and Sulphur dioxide
Nitrogen oxides and sulphur dioxide form the acids in acid rain.
The idea
Oxides of non-metals dissolve in water to give acids. Sulphur and nitrogen oxides give strong acids. Carbon dioxide gives only a weak one. Carbon monoxide and nitrogen gas give none.
Coal and oil burn → sulphur dioxide → Hot engines and furnaces → nitrogen oxides → Both dissolve in rain water → Sulphuric and nitric acid
Why the others are wrong
(a) Nitrogen gas is inert, and CO₂ only makes rain mildly acidic.
(b) CO forms no acid.
(c) Ozone forms no acid.
Also know
Nature adds some too: volcanoes give off sulphur dioxide and lightning makes nitrogen oxides. Strictly, “nitrous oxide” (N₂O, laughing gas) is not an acid-rain gas; the question uses the name loosely for nitrogen oxides. The real acid-rain gases are SO₂ and NO/NO₂.
🔒 Acid rain: NOₓ + SO₂.