In which condition is advection fog most likely to form?

Correct answer: Warm moist air moves over a cold surface

Correct answer: A. Advection means horizontal movement of air. Advection fog forms when warm, moist air is transported horizontally over a colder surface, such as cold land or cold ocean water. Contact with the cold surface cools the lower part of the moving air. If the air cools to its dew point, it becomes saturated and water vapour condenses on tiny particles into suspended droplets, producing fog. A is correct because it includes horizontal movement, moisture, and cooling over a cold surface. B is wrong because dry air lacks sufficient moisture and is not likely to form fog merely by remaining over hot desert ground. C is wrong because it describes neither the required moist air nor the usual horizontal cooling process. D is wrong because fog requires water vapour; removing all vapour prevents condensation. Memory cue: advection = air advects, or moves sideways, over a cold surface. Do not confuse it with radiation fog, which mainly results from local surface cooling and weak wind.