The capacity of the atmosphere to hold the maximum amount of water vapour primarily depends on which factor?

Correct answer: Air temperature

Direct answer: B, air temperature. The maximum water vapour that air can contain before becoming saturated is strongly controlled by temperature. Warm air has a higher saturation vapour pressure and can support more water vapour than cold air at the same pressure. If air is cooled to its dew point, it becomes saturated; further cooling can lead to condensation, cloud or fog formation. A is not the primary school-level control asked here, although pressure and density can affect atmospheric conditions. C does not directly set the saturation capacity of air, and D concerns ultraviolet radiation protection rather than water-vapour capacity. Do not confuse capacity with actual humidity: warm air may have a high capacity but contain little vapour, while cool air may be nearly saturated with less vapour. Memory cue: “warmer air can hold more vapour; cooling encourages condensation.”