What condition must occur for clouds, fog, or dew to form?

For clouds, fog, or dew to form, water vapor must condense. This process occurs when the air temperature cools to its dew point, allowing the water vapor in the air to transition from a gas to a liquid state, leading to the formation of tiny water droplets that make up clouds and fog, or moisture that settles on surfaces as dew.

While it is true that water vapor must be present in the atmosphere, the mere presence of it does not guarantee the formation of clouds, fog, or dew. Conditions need to be right for the water vapor to undergo condensation. When relative humidity reaches 100 percent, it indicates that the air is saturated with water vapor, which is a crucial condition for condensation to occur. However, this saturation must lead to an actual condensation of vapor for clouds or fog to form, making the process of water vapor condensation the critical step in their formation.

The statement about the temperature being below freezing can relate to frost formation, but it does not apply to all instances of clouds and fog, as these can occur in a variety of temperature conditions above freezing as well. Therefore, focusing on the condensation of water vapor provides the most direct reasoning for the formation of clouds, fog, or dew.