Final answer:
The temperature at which the air is fully saturated with moisture is known as the dew point, where the relative humidity reaches 100%, and condensation can occur, leading to the formation of fog.
Step-by-step explanation:
The temperature at which the air is completely saturated with moisture is best described by the dew point. This is the temperature at which air reaches 100% relative humidity, and additional water vapor will condense into liquid form. This condensation process releases latent heat of vaporization, which can prevent the temperature from dropping further. When the dew point is below freezing, we refer to it as the frost point.
Relative humidity is a measure of how much water vapor is present in the air compared to the maximum amount the air can hold at that temperature. As the temperature drops, so does the capacity of the air to hold moisture. When the air cools to the dew point temperature, saturation occurs, and fog can develop due to the condensation of water droplets.