Final answer:
When air temperature equals the dew point temperature, the air is saturated and the relative humidity is 100%, meaning no more water vapor can be held in the air.
Step-by-step explanation:
If the air temperature equals the dew point temperature (DPT), then the air is saturated and the relative humidity (RH) equals 100%. This is because at the dew point temperature, the amount of water vapor in the air has reached its maximum, known as the saturation vapor density, and the air cannot hold any more moisture. Any additional cooling would result in condensation of water vapor into dew. Therefore, if an air parcel has a temperature of 10.0°C and contains 9.40 g/m³ of water vapor, the dew point is also 10.0°C, indicating that the relative humidity is indeed 100% at this point.