As an air mass cools, water will condense when: a. the temperature reaches the dew point. b. the humidity reaches the dew point. c. the relative humidity equals the standard humidity. d. the air pressure reaches the atmospheric pressure.

Option A

Explanation:

The temperature at which water vapor mixes with air to saturate it is called as dew point temperature

At this point, the rate of following becomes equal -  

a)Condensation of gaseous water (water vapor)  

b)Evaporation of liquid water  

However, when the temperature becomes lower than the dew point temperature, then instead of gaseous water, liquid water starts condensing.

Hence, option A is correct

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