When can steam fog or evaporation fog form?

Correct answer: Cold air moves over warm water and gains moisture

Correct answer: A. Steam fog, also called evaporation fog, forms when relatively cold air passes over warmer water. Warm water adds moisture to the air through evaporation, while the air itself remains cool. Because cool air can reach saturation quickly, the added water vapour condenses into tiny droplets that appear as a fog resembling steam. A is correct because it supplies both required conditions: a warm moisture source and cold air capable of becoming saturated. B is wrong because dry sand does not provide the warm water needed to add abundant moisture. C is wrong because completely dry conditions lack the water vapour required for fog. D is wrong because condensation nuclei help water vapour form droplets; their absence would make droplet formation more difficult, not more likely. Memory cue: steam fog is “warm water meeting cold air.” The visible fog is not smoke; it is a cloud of tiny liquid water droplets near the surface.