Dew point temperature is defined as:

• A. Temperature at which a liquid boils at fixed pressure
• B. Temperature at which a vapor is saturated with its liquid
• C. Temperature at which vapor condenses completely at fixed pressure
• D. Temperature at which a vapor begins to condense at a fixed pressure

Answer: (D)

Humidity and condensation hinge on how much water vapor the air can hold. The dew point is that temperature at which the air becomes saturated with water vapor at a fixed pressure, so condensation begins. At this temperature, the vapor pressure of water equals the saturation vapor pressure, and any further cooling or addition of moisture causes water to start forming droplets on surfaces. This is different from the boiling point, which is about a liquid turning into vapor, and it’s about the onset of condensation rather than complete condensation. The dew point also corresponds to the moment when relative humidity reaches 100%.