Humidity of the air

Answer: (b) Decreases with the increase in atmospheric temperature

Warmer air can hold more water, so relative humidity falls when temperature rises.

The idea

Relative humidity compares actual water vapour with the saturation amount at the same temperature. Warming increases that saturation amount. If actual vapour stays unchanged, the relative humidity falls. Temperature alone does not determine whether the air gains or loses water vapour.

Air warms without added water vapour → Saturation vapour pressure rises → Actual vapour remains unchanged → Actual-to-saturation ratio falls → Relative humidity decreases

Why the others are wrong

(a) Absolute humidity may rise, but relative humidity falls.

The trap

Absolute vs relative humidity.

Also know

Specific humidity measures vapour mass relative to the mass of moist air. Absolute humidity measures vapour mass per unit volume and can also change when air expands. Cooling unchanged air raises relative humidity until dew point is reached. A warm humid coast can contain more vapour than a cold place even when its relative humidity is lower.