Final answer:
The maximum amount of water vapor air can hold, known as saturation vapor density, varies with temperature. At 20.0°C, the maximum is 17.2 g/m³, which corresponds to a partial pressure of 2.33 x 10³ Pa, indicative of 100% relative humidity.
Step-by-step explanation:
The maximum amount of water vapor that the air can hold at any given temperature and pressure is determined by the air's saturation vapor density at that temperature. When the partial pressure of water vapor in the air is equal to the vapor pressure of water at that temperature, no more water can enter the vapor phase, which means that air has reached its maximum capacity for containing water vapor. At 20.0°C, this saturation vapor density is 17.2 g/m³, which corresponds to a partial pressure of 2.33 x 10³ Pa.
Therefore, this is the maximum amount of water vapor that can exist in a cubic meter of air at this temperature without leading to condensation. This value represents the 100% relative humidity level for these conditions because it is at this point that equilibrium is established between the liquid and vapor phases of water.