ANS:A - Dew point

The term you're referring to is dew point. The dew point is the temperature at which a gas-vapor mixture becomes saturated when cooled at constant total pressure out of contact with a liquid. At this temperature, the vapor begins to condense into liquid phase, and further cooling will result in additional condensation. In contrast, the bubble point is the temperature at which a liquid-vapor mixture becomes saturated when heated at constant pressure. The dry bulb temperature is the temperature of air measured by a regular thermometer, and the wet bulb temperature is the temperature registered by a thermometer when its bulb is covered with a wet cloth and exposed to moving air. The dew point is the temperature at which air becomes saturated with water vapor when cooled at constant pressure and out of contact with additional liquid water. At this temperature, the air holds the maximum amount of moisture it can at that pressure, leading to condensation or dew formation. Here's how it works:

1. Water Vapor in Air: Air typically contains some amount of water vapor, even if it's not visibly humid. The amount of water vapor air can hold depends on its temperature. Warmer air can hold more moisture than cooler air.
2. Cooling the Air: When air is cooled, its capacity to hold moisture decreases. As the air cools, it reaches a point where it can no longer hold all the moisture it contains, and the excess moisture begins to condense into tiny water droplets. This is the dew point.
3. Formation of Dew: When the air reaches its dew point temperature, the moisture in the air starts to condense on surfaces, such as grass, leaves, or windows, forming dew. Dew is simply water vapor that has condensed into liquid water due to the air reaching its dew point.
4. Condensation in the Atmosphere: In the atmosphere, the dew point is important for understanding weather patterns and forecasting. When warm, moist air cools to its dew point, clouds can form as the water vapor condenses into liquid droplets around tiny particles in the air, such as dust or pollutants. Similarly, fog forms when the air near the surface cools to its dew point, causing water vapor to condense into tiny water droplets suspended in the air.

The dew point is a critical parameter in meteorology for predicting fog, frost, dew, and cloud formation, as well as for understanding humidity levels and the potential for precipitation. It is often used in conjunction with other weather variables to assess atmospheric stability and moisture content.