How is relative humidity defined?

Relative humidity is defined as the ratio of the current vapor pressure of water in the air to the saturation vapor pressure of water at a given temperature, expressed as a percentage. This measurement indicates how close the air is to being saturated with moisture. When the relative humidity is at 100%, it means the air cannot hold any more water vapor, leading to conditions such as condensation or precipitation. Understanding relative humidity is crucial in the context of drying processes since it affects evaporation rates and the efficiency of dehumidification methods.

Other options do not accurately describe relative humidity; for example, total moisture in the air relates to absolute humidity, while moisture in the soil does not pertain to air humidity at all. The humidity percentage at room temperature does not account for the critical factor of saturation pressure, which is essential for understanding relative humidity.