The correct option is Fog.
Explanation
Condensation is the process by which water vapour in the air transforms into liquid water. When this occurs in the lower atmosphere, the water vapour condenses around hygroscopic nuclei-such as dust, smoke, and salt particles-suspended in the air.Detailed Analysis:
- Fog (Correct): Fog forms when the temperature of an air mass containing a significant amount of water vapour drops suddenly. This cooling causes condensation to take place on fine dust particles suspended within the air mass itself. Fog is essentially a cloud with its base at or very near the ground, leading to reduced visibility.
- Dew (Incorrect): Dew occurs when moisture is deposited in the form of water droplets on cooler surfaces of solid objects (such as grass blades, leaves, or stones), rather than on particles suspended in the air. It typically forms under conditions of clear skies, calm air, and cold ground surfaces.
- Frost (Incorrect): Frost occurs when condensation takes place on cold surfaces while the dew point is at or below the freezing point ($0^\circ \text{C}$). The moisture deposits directly as ice crystals (sublimation) on the surface.
- Hail (Incorrect): Hail is a form of solid precipitation consisting of ice pellets. It is formed within cumulonimbus clouds due to strong vertical updrafts and falls to the ground, distinct from surface-level condensation phenomena.
Key Takeaway:
The defining characteristic of fog is that condensation occurs on suspended nuclei (dust/smoke) within the air mass, whereas dew and frost involve condensation directly onto solid surfaces.