If the ground cools rapidly on a clear calm night and the lower moist air remains stable what is the best explanation of the fog formed?

Correct answer: Radiational cooling brought lower air to dew point

Correct answer: B, radiational cooling brought the lower air to its dew point. On a clear night, the ground loses heat by emitting terrestrial radiation, and it cools rapidly because clouds are not present to return much heat. Calm conditions prevent strong mixing, so the moist air touching or lying just above the ground is cooled efficiently. When its temperature reaches the dew point, relative humidity becomes effectively 100 percent and water vapour condenses into tiny droplets, producing radiation fog. A is wrong because sea fog is associated with moist air moving over a colder surface, not simply high waves. C is wrong because orographic fog results when air is forced up a slope and cools by expansion. D is wrong because fog requires moisture, not its absence. Memory cue: clear sky plus calm air plus night cooling points to radiation fog.