Consider the following statements related to water vapours :
1. It is a variable gas in the atmosphere, which decreases with altitude
2. In the dry and cold areas of desert and polar regions, it may be less than one per cent of the air
Which of the statements given above is/are correct ?

Both statements are correct according to standard physical geography (NCERT Class XI).

• Statement 1 is correct: Water vapour is a variable gas in the atmosphere. Its concentration decreases with altitude because the air's capacity to hold moisture decreases as temperature and pressure drop. Approximately 90% of atmospheric water vapour is concentrated in the lowest 5 km of the atmosphere.
• Statement 2 is correct: The distribution of water vapour varies geographically. In warm and wet tropical regions, it may account for nearly 4% of the air by volume. However, in dry and cold regions such as deserts and polar areas, it constitutes less than 1% of the air.

Water vapour is also a significant greenhouse gas, as it absorbs parts of the incoming solar radiation and preserves the Earth’s radiated heat, thereby acting like a blanket.