SSC CHSL 2025 PYQ — Question 87

The correct answer is Option 3: Both I and II.
Explanation:

• Cooling due to evaporation occurs when a liquid absorbs heat (specifically, the Latent Heat of Vaporization) from its surrounding environment or surface in order to vaporize. This causes the temperature of that surface to drop, resulting in a sensation of coolness.
• Both of the given points serve as precise examples of this very process:
• Pouring acetone on the palm: Acetone is a highly volatile liquid. When you pour it onto your palm, it draws energy (heat) from your palm to facilitate its evaporation, making your palm feel cool.
• Sprinkling water on the roof: During summer days, the roof becomes extremely hot. When water is sprinkled on the roof, it absorbs the heat from the roof to convert into vapor. Consequently, the roof cools down.

Other significant examples of cooling through evaporation (Quick Revision):

• Water in an earthen pot: The surface of an earthen pot (Matka) contains tiny pores through which water continuously seeps out and evaporates. This evaporation draws heat from the water inside the pot, thereby keeping the water cool.
• Sweating: When we sweat, the perspiration absorbs heat from our skin and evaporates; this process lowers our body temperature and provides a cooling sensation.
• Wearing cotton clothes: In the summer, cotton clothes absorb sweat and facilitate its evaporation by exposing it to the air, thereby helping to keep the body cool.

Important Questions for Upcoming Exams:
Question: What factors determine the rate of evaporation?
Answer: Surface area (the rate increases as the surface area increases), temperature, humidity (the rate increases as humidity decreases), and wind speed.
Question: Is evaporation a surface phenomenon?
Answer: Yes, it occurs only from the surface.
Question: Why does water in an earthen pot remain cool during the summer?
Answer: Due to the cooling process caused by evaporation.