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:
Answer & explanation
Answer: (a) 1 only
Water vapour is a variable gas concentrated near the surface, so it thins out with height. It is most plentiful in the warm, wet tropics (up to about 4% of air by volume) and scarcest in cold, dry polar and desert air (under 1%).
- ✓ 1. Water vapour is a variable gas whose amount decreases with altitude, because evaporation happens at the surface and cold upper air holds little moisture.
- ✗ 2. Its share is lowest, not highest, at the poles — below 1% of the air — and highest in the warm, wet tropics at about 4%.
Remember · Water vapour: up to ~4% of air in humid tropics, under 1% in polar and desert air; decreases with altitude and from equator to poles.
📘 Read it in NCERT: Class 11 Fundamentals of Physical Geography, Ch 7 (practise this chapter)
Sources
- NCERT Class 11 · Fundamentals of Physical Geography, Chapter 7 “Water vapour is also a variable gas in the atmosphere, which decreases with altitude. In the warm and wet tropics, it may account for four per cent of the air by volume, while in the dry and cold areas of desert and polar regions, it may be less than one per cent of the air.”
Question and answer: UPSC's official GS Paper I (2024, Series A) — paper ↗ · answer key ↗. Explanation: Minimalist IAS, checked 30 Sept 2026 (how we verify). ·