Explanation:

It is formed when the condensation occurs below the freezing point
Fog is formed when there is a difference of less than 2.5 °C between the air temperature and the dew point, which is the temperature below which water droplets start to condense and form dew. When water vapor condenses, it turns into tiny droplets of water that are suspended in the air. Water vapor exists in the atmosphere for various reasons, including the evaporation of water from water bodies, transpiration from plant leaves, and the movement of air over warm bodies of water.