The sudden transformation of mountain fog into dense clouds is considered the result of which physical state of the water cycle?

Correct answer: Air rising and undergoing adiabatic cooling

Correct answer: A, air rising and undergoing adiabatic cooling. Moist air moving up a mountain slope enters regions of lower atmospheric pressure. It expands, and expansion causes the air to cool without requiring direct heat loss to the surroundings; this is called adiabatic cooling. If the air cools to its dew point, some water vapour condenses into tiny liquid droplets. These droplets make fog or cloud denser. Option A is correct because it includes both the important upward movement and the cooling that produces condensation. Option B may add water vapour, but evaporation alone does not explain the cooling and cloud formation. Option C would usually reduce condensation because warm air can hold more vapour. Option D concerns movement of underground water and does not form clouds. Memory cue: moist air rising over mountains becomes cooler, reaches saturation, and condenses.