Assertion (A): The amount of moisture in the atmosphere is related to latitude. Reason (R): The capacity to hold moisture in the form of water vapour is related to temperature.

Answer: (a) Both A and R are individually true and R is the correct explanation of A

Warmer (lower-latitude) air can hold more vapour, so moisture falls with latitude.

The idea

The saturation amount of water vapour increases with temperature. Warm tropical conditions therefore allow much more vapour than cold polar conditions. Latitude affects the broad temperature pattern, linking it indirectly to atmospheric moisture. Actual moisture also depends on evaporation and air movement, so latitude is not its only control.

Latitude affects average solar heating → Heating affects air temperature → Warmer conditions have higher saturation vapour pressure → Evaporation can supply more vapour → Tropical air commonly contains more moisture than polar air

Why the others are wrong

(b) R explains A.

(c) R is true.

(d) A is true.

Also know

Relative humidity is a percentage of saturation, so cold air can have high relative humidity while containing little vapour. Specific humidity measures actual vapour mass relative to moist-air mass. Dew point is a useful indicator of actual moisture content. A hot desert may have low actual humidity despite the high saturation amount possible at its temperature.