If visibility becomes very low and nearly less than (1) kilometre, it is generally associated with what?

Correct answer: Fog

Direct answer: A, fog. Fog is a cloud-like collection of very small water droplets suspended close to the ground. These droplets scatter and partly absorb light, so distant objects become difficult to see. Very low visibility, commonly described as below about one kilometre in school geography, is therefore a useful practical sign of fog. A is correct because fog occupies the air near the observer and directly reduces horizontal visibility. B is incorrect because dew forms as liquid water on surfaces such as grass and leaves; it does not usually fill the air and obstruct distant vision. C is incorrect because clear skies normally allow better visibility, although dust or smoke can create other conditions. D is incorrect because a dry hot wind is not a fog-forming, moisture-rich condition. Memory cue: fog is essentially a cloud at ground level, so poor visibility is its key clue.