With reference to the formation of clouds, consider the following statements: 1. Clouds are formed when water vapour in the air condenses at high altitudes. 2. At high altitudes, the air becomes too warm for condensation to occur. 3. Clouds are composed entirely of water vapour and not liquid droplets. Which of the statements given above is/are correct?

The correct option is (a). Explanation Clouds are visible aggregates of minute water droplets or ice crystals suspended in the atmosphere. Their formation is primarily driven by the cooling of air masses, which reduces the air's capacity to hold water vapour, leading to saturation and subsequent condensation. Statement-wise Analysis: - Statement 1 is Correct: Clouds form when warm, moist air rises. As the air ascends, it expands due to decreasing atmospheric pressure, leading to adiabatic cooling. When the air temperature drops to the dew point, water vapour condenses onto hygroscopic nuclei (such as dust or salt particles) to form clouds. - Statement 2 is Incorrect: In the troposphere, where most clouds form, temperature generally decreases with altitude (Normal Lapse Rate). The air becomes cooler at higher altitudes, which is the necessary condition for condensation to occur. If the air became warmer, it would hold more moisture as vapour rather than condensing it. - Statement 3 is Incorrect: Water vapour is an invisible gas. Clouds are visible because they are composed of liquid water droplets or ice crystals. If clouds were composed entirely of water vapour, they would be invisible to the naked eye. Key Takeaway: Clouds are formed by the condensation of water vapour into liquid droplets or ice crystals due to the cooling of air at higher altitudes. Water vapour itself is invisible; clouds are the visible result of its phase change.

With reference to the formation of clouds, conside... - NCERT Class 6 Environment & Ecology MCQ

Solution

The correct option is (a).

Explanation

Clouds are visible aggregates of minute water droplets or ice crystals suspended in the atmosphere. Their formation is primarily driven by the cooling of air masses, which reduces the air's capacity to hold water vapour, leading to saturation and subsequent condensation.

Statement-wise Analysis:

Statement 1 is Correct: Clouds form when warm, moist air rises. As the air ascends, it expands due to decreasing atmospheric pressure, leading to adiabatic cooling. When the air temperature drops to the dew point, water vapour condenses onto hygroscopic nuclei (such as dust or salt particles) to form clouds.
Statement 2 is Incorrect: In the troposphere, where most clouds form, temperature generally decreases with altitude (Normal Lapse Rate). The air becomes cooler at higher altitudes, which is the necessary condition for condensation to occur. If the air became warmer, it would hold more moisture as vapour rather than condensing it.
Statement 3 is Incorrect: Water vapour is an invisible gas. Clouds are visible because they are composed of liquid water droplets or ice crystals. If clouds were composed entirely of water vapour, they would be invisible to the naked eye.

Key Takeaway:
Clouds are formed by the condensation of water vapour into liquid droplets or ice crystals due to the cooling of air at higher altitudes. Water vapour itself is invisible; clouds are the visible result of its phase change.

NCERT Class 6 Environment & Ecology — Chapter 1: Water

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