With reference to "water vapour", which of the following statements is/are correct ? 1. It is a gas, the amount of which decreases with altitude. 2. Its percentage is maximum at the poles. Select the answer using the code given below :
- (a) 1 only ✓ UPSC's answer
- (b) 2 only
- (c) Both 1 and 2
- (d) Neither 1 nor 2
Why the answer is (a)
• Water vapour is the gaseous form of water and the most variable constituent of the atmosphere, ranging from near zero to about 4% by volume.
• Statement 1 is correct: about 90% of atmospheric water vapour lies below 5 km, and its amount falls sharply with altitude as the air becomes colder and thinner.
• Statement 2 is wrong: warm air can hold far more moisture than cold air, so water vapour is maximum in the humid tropics and minimum over the cold poles and deserts.
• Water vapour is also the most important natural greenhouse gas and the source of all clouds and precipitation.
• Hence 1 only, option (a).
Why the other options are wrong
- (b) 2 only
- Statement 2 is wrong: water vapour peaks in the tropics, not the poles.
- (c) Both 1 and 2
- Statement 2 is wrong, so both cannot be correct.
- (d) Neither 1 nor 2
- Statement 1 is correct: water vapour decreases with altitude.
Asked in the GS Paper I of the UPSC Civil Services Preliminary Examination 2024, held on 16 June 2024. Question and answer key: Union Public Service Commission. Explanation: UPSC Answer Check.