Clouds
Explanation
Condensation is the process by which water vapour in the air transforms into liquid water. This process occurs when the temperature of the air drops to the dew point or when the air becomes saturated with moisture. The form taken by the condensed water depends largely on the altitude at which the process occurs and the surface on which condensation takes place.
Option-wise Analysis
- Dew is Incorrect: Dew is formed when moisture is deposited in the form of water droplets on cooler surfaces of solid objects (such as stones, grass blades, and plant leaves) rather than on nuclei in the air. This phenomenon occurs at ground level.
- Fog is Incorrect: Fog is essentially a cloud with its base at or very near the ground. It consists of tiny water droplets suspended in the air near the earth's surface, reducing visibility.
- Clouds is Correct: Clouds are formed by the condensation of water vapour around hygroscopic nuclei (such as dust particles) at considerable elevations (high altitudes). As air rises, it expands and cools; when the temperature falls below the dew point, water vapour condenses to form clouds.
- Frost is Incorrect: Frost forms on solid surfaces at ground level when the dew point is at or below the freezing point. It consists of minute ice crystals formed directly from water vapour (deposition) rather than liquid droplets.
Key Takeaway
Clouds are the result of condensation occurring at higher altitudes in the atmosphere, whereas dew, fog, and frost are condensation or deposition phenomena that occur near the Earth's surface.