UPSC Prelims 2010 Q38: Environment & Ecology – Pollution & Waste Management
Consider the following:
1. Oxides of Hydrogen
2. Oxides of Nitrogen
3. Oxides of Sulphur
Which of the above causes/cause acid rain?
- (a) 1 and 2 only
- (b) 3 only
- (c) 2 and 3 only
- (d) 1, 2 and 3
Answer: (c) 2 and 3 only
Explanation
What causes acid rain
Acid rain results from specific atmospheric pollutants reacting with water vapour.
| Pollutant | Verdict | Reason |
|---|---|---|
| 1. Oxides of Hydrogen | Incorrect | 'Oxides of hydrogen' essentially means water itself; this is not an acid-rain-causing pollutant |
| 2. Oxides of Nitrogen | Correct | NOx (from vehicles, industry) reacts with atmospheric moisture to form nitric acid, a major acid rain component |
| 3. Oxides of Sulphur | Correct | SOx (from burning fossil fuels) reacts with water vapour to form sulphuric acid, the other major acid rain component |
Acid rain chemistry:
| Point | Detail |
|---|---|
| Key pollutants | Oxides of nitrogen (NOx) and sulphur (SOx) |
| Reaction | React with atmospheric water vapour to form acids |
| Not a cause | 'Oxides of hydrogen' (essentially water) play no causal role |
Answer: (c) 2 and 3 only.
Why each option is right or wrong
- (a) Incorrect. 'Oxides of hydrogen' (statement 1) do not cause acid rain; this pairing wrongly includes it.
- (b) Incorrect. Oxides of nitrogen (statement 2) are also a major cause, so '3 only' is incomplete.
- (c) CORRECT. Oxides of nitrogen and sulphur are the two primary pollutants reacting with atmospheric moisture to form acid rain.
- (d) Incorrect. Statement 1 ('oxides of hydrogen') is not a real cause, so 'all three' is wrong.
Key point
Acid rain is caused by OXIDES OF NITROGEN (NOx) and OXIDES OF SULPHUR (SOx) reacting with atmospheric moisture — 'oxides of hydrogen' (essentially water) play no such role.
Remember
Acid rain causes: oxides of nitrogen and oxides of sulphur — not 'oxides of hydrogen', which is essentially just water.
Common mistakes
- Being misled by the unusual phrase 'oxides of hydrogen', which is essentially just water, not a pollutant.
- Missing that both NOx and SOx contribute to acid rain, not just one of them.
- Not connecting these specific oxides to their respective acids (nitric and sulphuric).
Exam tip
Acid rain = NOx + SOx reacting with atmospheric water vapour → nitric + sulphuric acid. 'Oxides of hydrogen' is a distractor, not a real pollutant category.
Sources
- Central Pollution Control Board — National Ambient Air Quality Standards (November 2009)
- NCERT Class XI Chemistry — Environmental Chemistry (acid rain)