Why may rainfall not occur even when visibility is low in fog?

Correct answer: Fog droplets are tiny and suspended

Direct answer: C is correct. Fog is made of tiny water droplets suspended close to the ground, so it can reduce visibility strongly. However, these droplets are usually too small and too widely separated to fall as rain. Rain requires droplets or ice particles to grow sufficiently large that gravity overcomes air resistance and they descend to the ground. Growth may occur through collision and coalescence or other cloud processes, but fog does not automatically undergo enough growth for rainfall. A is wrong because fog contains liquid water droplets. B is wrong because the droplets scatter light and therefore directly reduce visibility. D is wrong because fog is associated with moist, nearly saturated air, not always dry air. The distinction is size and fall, not simply the presence of water: fog can be wet and opaque while still producing no measurable rain. Memory cue: low visibility does not necessarily mean large falling drops.