When dense tiny water droplets in the lower atmosphere greatly reduce visibility, what condition is it called?

Correct answer: Fog

Direct answer: C, fog. Fog is a dense collection of very small condensed water droplets suspended in the air close to Earth’s surface. These droplets scatter light in many directions, so distant objects become difficult to see and visibility falls greatly. Dew is different because its liquid droplets are deposited directly on a cool surface. Frost is a coating of ice crystals on a cold surface, usually under freezing conditions. Mist also contains airborne droplets, but it is generally less dense than fog and causes a smaller reduction in visibility. Therefore the combination of “lower atmosphere,” “dense droplets,” and “greatly reduced visibility” identifies fog. A is wrong because dew is surface-based. B is wrong because frost is solid ice on a surface. D is the closest distractor, but the clue “greatly” and the dense collection indicate fog rather than the lighter condition of mist. Memory cue: fog is thicker airborne water; mist is thinner airborne water.