Consider the following:
- 1.Carbon monoxide
- 2.Nitrogen oxide
- 3.Ozone
- 4.Sulphur dioxide
Excess of which of the above in the environment is/are cause(s) of acid rain?
Answer & explanation
Answer: (b) 2 and 4 only
Nitrogen oxides and sulphur dioxide cause acid rain: in the air they turn into nitric and sulphuric acids that fall with rain. Carbon monoxide and ozone are pollutants too, but they do not form these acids.
- ✓ 2. Nitrogen oxides (NOx) react with water, oxygen and other chemicals in the air to form nitric acid.
- ✓ 4. Sulphur dioxide (SO2) reacts with water, oxygen and other chemicals in the air to form sulphuric acid.
- ✗ 1. Carbon monoxide is a poisonous gas from incomplete burning of fuel; it is not one of the gases that make acid rain.
- ✗ 3. Ozone near the ground harms lungs and plants but is not an acid-rain gas.
Remember · Acid rain = SO2 + NOx turning into sulphuric and nitric acids; rain with pH below 5.6 is called acid rain.
📘 Read it in NCERT: Class 11 Political Theory, Ch 3 (practise this chapter) · Class 10 Science, Ch 2 (practise this chapter)
Sources
- US EPA — What is Acid Rain? ↗ “Acid rain results when sulfur dioxide (SO 2 ) and nitrogen oxides (NO X ) are emitted into the atmosphere and transported by wind and air currents.”
- NCERT Class 11 · Political Theory, Chapter 3 “They also account for three-quarters of emissions of sulphur and nitrogen oxide that cause acid rain.”
- NCERT Class 10 · Science, Chapter 2 “When pH of rain water is less than 5.6, it is called acid rain.”
Question and answer: UPSC's official GS Paper I (2022, Series A) — paper ↗ · answer key ↗. Explanation: Minimalist IAS, checked 30 Sept 2026 (how we verify). ·