Why can fog form when relatively warm moist air moves over cold water?

Correct answer: Air cooling by contact and condensing

Correct answer: B. A relatively warm, moist air mass contains water vapour. As it moves over colder water, the air in contact with the water loses heat. Its temperature may fall to the dew point, at which the air becomes saturated. Excess water vapour then condenses on condensation nuclei into tiny suspended droplets, creating fog. B is correct because it gives both essential steps: cooling by contact and condensation. A is wrong because the air is being cooled, not warmed and dried; drying would generally reduce relative humidity. C is wrong because salt formation is not the process that makes fog. D is wrong because water vapour is necessary for the droplets to form. The exact development also depends on moisture, temperature difference, wind, and mixing, but the central mechanism remains cooling to saturation. Memory cue: warm moist air crossing a colder surface loses heat and may become fog.