Q27 · UPPSC Prelims 2024 · Set A · General Studies

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Given below are two statements, one is labelled asAssertion (A) :and the other as Reason (R).Assertion (A):Relative humidity decreases with increasing air temperature.Reason (R):Absolute humidity increases with increasing evaporation.Select the correct answer from the codes given below:

A Both (A) and (R) are true, but (R) is not the correct explanation of (A).
B (A) is false, but (R) is true.
C Both (A) and (R) are true and (R) is the correct explanation of (A).
D (A) is true, but (R) is false.

Correct answer: (a) Both (A) and (R) are true, but (R) is not the correct explanation of (A).

Explanation

  1. A

    Both (A) and (R) are true, but (R) is not the correct explanation of (A).

    Both (A) and (R) are true, but (R) is not the correct explanation of (A). Assertion (A) is correct because warmer air has a greater capacity to hold moisture, so as temperature rises while actual water vapor remains constant, relative humidity drops. Reason (R) is also correct because increased evaporation adds more moisture to the air, raising absolute humidity. However, the reason for relative humidity decreasing is the rising temperature itself changing the air's moisture capacity, not the rate of evaporation alone, making this option the officially designated correct key.

  2. B

    (A) is false, but (R) is true.

    (A) is false, but (R) is true. This option incorrectly claims that the assertion about relative humidity decreasing with temperature is false. In reality, warm air increases saturation capacity, which directly causes relative humidity to decline when moisture content is unchanged.

  3. C

    Both (A) and (R) are true and (R) is the correct explanation of (A).

    Both (A) and (R) are true and (R) is the correct explanation of (A). This option incorrectly links the increase in absolute humidity due to evaporation as the governing cause for the drop in relative humidity as temperature rises. The actual driver of relative humidity change in the assertion is the temperature-dependent moisture holding capacity of the air itself.

  4. D

    (A) is true, but (R) is false.

    (A) is true, but (R) is false. This option wrongly dismisses the reason statement as false when absolute humidity indeed rises alongside enhanced evaporation rates. Therefore, stating that the reason is false contradicts established meteorological principles regarding water vapor.

Summary. Official key is (a) Both (A) and (R) are true, but (R) is not the correct explanation of (A). The assertion correctly notes that relative humidity falls when air temperature increases because warmer air can hold more water vapor. The reason correctly identifies that absolute humidity increases when evaporation rates go up. Both statements describe valid atmospheric science principles independently. However, the rising evaporation does not explain why relative humidity drops with temperature. Thus, both statements hold true, but the second does not explain the first.