Introduction:
When air is nearly saturated and the temperature drops, a phenomenon called the dew point is reached. The dew point is the temperature at which the air becomes saturated and condensation occurs.

Explanation:
1. Saturation:
When air is nearly saturated, it means that it contains a high amount of moisture or water vapor. The capacity of air to hold water vapor increases with temperature. When the air reaches its maximum capacity to hold water vapor at a particular temperature, it becomes saturated.

2. Temperature drop:
When the temperature drops, the capacity of the air to hold water vapor decreases. As the air cools down, it becomes less capable of holding the same amount of moisture. This leads to a situation where the air is holding more moisture than it can handle, resulting in condensation.

3. Dew point:
The dew point is the temperature at which the air becomes saturated and condensation occurs. It is the temperature at which the air reaches 100% relative humidity. When the temperature drops below the dew point, the excess moisture in the air condenses and forms dew, fog, or clouds.

4. Condensation:
Condensation is the process by which water vapor changes from a gas to a liquid. It occurs when the air becomes saturated and cannot hold any more moisture. The excess moisture condenses into tiny water droplets or ice crystals, forming clouds, fog, or dew.

Conclusion:
When air is nearly saturated and the temperature drops, the dew point is reached. At the dew point, the air becomes saturated and condensation occurs, leading to the formation of dew, fog, or clouds. Understanding the dew point is important in meteorology as it helps predict weather conditions and the formation of precipitation.