Question

The ratio of partial pressure of water vapour in a mixture to the saturation pressure of water at the same temperature of the mixture is called as ___________.
A)Humidity
B)Partial Humidity
C)Specific Humidity
D)Relative Humidity

Answer 1

Hint: This is an indicator of the probability of precipitation, dew, or fog.
For health and comfort, the ideal level of humidity is between 30-50 per cent.
This amount of humidity in the air depends on the amount of water in the air as well as the temperature of the air.

Complete answer:
The relative humidity of the air-water mixture is defined as the ratio of the partial pressure of the water vapour in the mixture to the equilibrium vapour pressure of the water over the flat surface of the pure water at a given temperature.
Relative humidity is usually expressed in terms of a percentage. If it is a higher percentage, it means that the air-water mixture is more humid. At 100 percent relative humidity, the air is saturated at its point of dew.
Relative humidity is an important metric used in weather forecasting and reporting. During summer weather when it is really hot, the increase in relative humidity thereby increases the evident temperature of humans as well as other animals by halting the evaporation of perspiration from the skin.

Following are the given alternatives:

1)Humidity is the concentration of water vapour in the air. Water vapour, the gaseous state of water, is usually invisible to the human eye. Humidity indicates the likelihood of precipitation, dew, or fog being present. Thus, Option A is incorrect.

2)Water vapour pressure is a partial pressure due to the water vapour in the wet gas mixture. Dalton's Law on Partial Pressures states that the total pressure in the gas is the sum of all the partial pressures of the constituents. Thus, Option B is incorrect.

3)The weight of the water vapour per unit weight of the air is called specific humidity. Thus, Option C is incorrect.

4)Relative humidity (RH) can be understood as the ratio of the partial pressure of the water vapour to the equilibrium vapour pressure of the water at the stated or given temperature. Thus, Option D is correct.

Hence, the correct answer is option (D)

Note: Relative humidity of 75 per cent means that the air holds 80 percent of the water it can hold at that temperature and pressure. As the air cools, it can no longer hold as much water as the relative humidity increases.
Relative humidity also measures water vapour, but RELATIVE to air temperature.
Relative humidity is mentioned in the weather forecast as it affects how we feel the temperature.