The correct option is It is frequent over mountains..
Explanation
Mist is a form of condensation occurring near the Earth's surface, where tiny water droplets remain suspended in the air. It is distinguished from fog primarily by its moisture content and visibility levels.
- It contains less moisture than fog. is Incorrect: Mist contains more moisture than fog. In mist, each condensation nucleus contains a thicker layer of moisture, whereas fog is comparatively drier.
- It is formed when dew point is below freezing. is Incorrect: When the dew point falls below the freezing point, condensation results in the formation of frost (minute ice crystals), not mist.
- It is frequent over mountains. is Correct: Mist is frequent over mountains. This phenomenon occurs as rising warm air moves up the slopes and meets a cold surface, causing the air to cool and condense into mist.
- It is a high-altitude cloud. is Incorrect: Mist is a surface-level phenomenon, similar to fog, rather than a high-altitude cloud. While the condensation process is similar to cloud formation, mist forms near the ground.
Key Takeaway: The primary distinction between mist and fog is that mist contains more moisture and typically allows for visibility between 1 km and 2 km, whereas fog is drier and reduces visibility to less than 1 km.