How is relative humidity defined?

Relative humidity is defined as the percentage of moisture in the air compared to the maximum amount of moisture the air can hold at a given temperature. It is expressed as a percentage, which reflects how much water vapor is present in the air relative to its capacity to hold water vapor at that specific temperature. This measurement is crucial for understanding weather processes, comfort levels in different environments, and the potential for precipitation.

While the amount of water vapor in the air is important, relative humidity specifically frames this amount as a percentage of the air's capacity for moisture, directly linking temperature and water vapor saturation. Therefore, defining relative humidity as the percent of water in the air accurately captures this concept, making it the correct choice.