As the temperature of an air mass decreases, the ____________.

As the temperature of an air mass decreases, the ability of the air to hold moisture decreases, which leads to an increase in relative humidity. Relative humidity is defined as the ratio of the current amount of water vapor in the air to the maximum amount of water vapor the air can hold at a given temperature. Cooler air can hold less water vapor than warmer air, so as the temperature decreases, the relative humidity increases, provided the amount of actual water vapor in the air remains constant.

In this context, if the air cools while maintaining the same moisture content, the relative humidity will rise, potentially reaching saturation and leading to condensation, clouds, or precipitation if the process continues. The other options relate to different aspects or behaviors of air and humidity which do not align with the principle governing relative humidity in relation to temperature.