What does relative humidity indicate?
a. how close air is to saturation
b. the amount of heating needed for evaporation
c. the amount of water vapor in the air
d. the ratio of water vapor to carbon dioxide in air

Ans A. how close air is to saturation

In general, humidity indicates the moisture content or the amount of water vapor in the air.

Relative humidity (RH) is the ratio of the amount of water vapor in the air to the amount of water vapor that the air can hold at that temperature.

RH = [Actual vapor density/Saturation Vapor density] *100

Relative humidity is temperature dependent. Higher the temperature, lower will be the value because high temperature will heat up the air causing it to expand. This will improve its ability to hold moisture thereby increasing the saturation vapor density and lowering the relative humidity.

Therefore, relative humidity indicates how close air is to saturation.