Final answer:
The limit at which air can contain no more moisture for a given temperature is known as saturation; at this point, the relative humidity is 100%, and the temperature is the dew point. Saturation is related to the vapor pressure of water, not the air's properties.
Step-by-step explanation:
The limit at which air contains as much moisture as it can hold for a given temperature is called the point of saturation. When air reaches this point, the relative humidity is 100%, meaning the air is fully saturated with water vapor and evaporation is inhibited. The dew point is the temperature at which the air is saturated, and any further cooling may result in condensation, forming dew or fog. The capacity for air to hold water vapor is mainly a function of temperature, with warmer air capable of holding more water vapor than cooler air.
The concept of air holding water vapor, however, is a simplification. What actually happens is that the amount of water vapor in air is determined by the vapor pressure of water. This capacity is unaffected by the properties of the air itself. If the partial pressure of water vapor in the air is less than the vapor pressure, water will evaporate until equilibrium is reached. Conversely, if the partial pressure exceeds the vapor pressure, condensation occurs.