When temperatures are below freezing, the temperature at which air becomes saturated leading to the formation of frost is the

The answer is Frost Point.

Explanation:

The temperature to which the air must be cooled, with constant pressure, to reach saturation (in relation to liquid water), is called the dew point. The dew point gives a measure of the water vapor content in the air. The higher, the greater the concentration of water vapor in the air. However, when cooling produces saturation at a temperature of 0 ° C or less, the temperature is called a frost point. The water vapor is deposited as frost on a surface whose temperature is below the dew point.

the answer for sodium is 0.186

the answer for rubidium is 0.251