Why can fog persist during temperature inversion near the surface?

Correct answer: Cold moist air remains trapped below

Answer: A, cold moist air remains trapped below. Normally, air temperature often decreases with height, allowing some vertical mixing. During a temperature inversion, a layer of warmer air lies above cooler air near the ground. This warmer layer acts like a lid and suppresses upward movement and mixing of the cold surface air. If the trapped air is moist and has cooled to or near its dew point, water vapour condenses into tiny droplets, producing fog. Because fresh, drier air cannot easily mix in and sunlight may be weak, the fog can last for a long time. A is correct because it identifies both the important conditions: low-level cold air and moisture trapped beneath the inversion. B is wrong because moisture remains in the lower air rather than escaping to space. C is wrong because rapid ground heating would usually help evaporation or mixing and may clear fog. D is wrong because vapour formation does not simply stop; condensation and evaporation depend on conditions. Memory cue: inversion means a warm lid over cool, moist air.