In which condition is dew more likely than fog?

Correct answer: Saturation is limited to the vicinity of a cold surface

Correct answer: A. Dew forms when cooling and saturation are concentrated at a surface, such as grass or a roof. The nearby air may be moist enough for droplets to deposit on that cold surface, while the larger layer of air above remains unsaturated and relatively clear. Fog, in contrast, requires many droplets to remain suspended through a shallow layer of air near the ground. Option A therefore describes conditions favouring dew rather than fog: saturation is restricted to the immediate surface zone. Option B is more consistent with fog because a deep lower-air layer is saturated. Option C can favour fog when cold air is trapped and becomes saturated in a valley, so it is not the best answer. Option D is an effect commonly associated with fog, not a condition favouring only dew. The important comparison is the vertical extent of saturation. Memory cue: “Surface saturation gives dew; air-layer saturation gives fog.”