Q. Given below are two statements, one is labelled as Assertion (A) and the other as Reason (R).
Assertion (A): Evaporation of sweat from human skin dissipates body heat.
Reason (R) : High humidity on a hot day increases discomfort.
Select the correct answer from the code 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) (A) is true, but (R) is false
d) Both (A) and (R) are true and (R) is the correct explanation of (A)
Correct Answer: a) Both (A) and (R) are true, but (R) is not the correct explanation of (A)
Question from UPPSC Prelims 2025
Explanation:
Assertion (A) is true: Evaporation of sweat removes latent heat from the skin. The phase change from liquid to vapor requires energy (latent heat of vaporization), which is taken from the body, thereby cooling it and dissipating body heat.
Reason (R) is also true: High humidity reduces the rate of evaporation because the air is already moist, diminishing the vapor pressure gradient. With less evaporation, the body cools less effectively, leading to greater discomfort on hot, humid days.
However, (R) does not correctly explain (A). (R) describes a related consequence (why discomfort increases in humidity) rather than explaining the mechanism of how evaporation dissipates heat. A proper explanation of (A) would mention latent heat removal, not humidity effects.
