Question

Select the correct statements:
(A) Increase in relative humidity decreases the density of air
(B) Increase in relative humidity decreases the rate of evaporation of water
(C) Increase in relative humidity decreases the velocity of sound
(D) Increase in relative humidity increases the velocity of sound

(A) I,II,IV
(B) I,II,III
(C) I,II
(D) I,IV

Answer 1

Hint:To solve this we must know that relative humidity is the ratio of partial pressure of water vapour to the equilibrium pressure of water vapour at a particular temperature. Relative humidity depends on the temperature and pressure of the system. In cold air, the same amount of water vapour causes a higher relative humidity than that in warm air.

Complete step-by-step solution:We know that the moisture content of the air is known as the humidity. The relative humidity is the ratio of partial pressure of water vapour to the equilibrium pressure of water vapour at a particular temperature.

The density of air varies with the relative humidity. When the amount of moisture in the air increases the amount of oxygen and nitrogen per unit volume in the air decreases. Thus, the mass of air per unit volume decreases and as a result the density of air decreases.
Thus, the statement ‘increase in relative humidity decreases the density of air’ is correct.

Relative humidity is the amount of moisture in the air compared to the moisture that air can hold at that temperature. When relative humidity is high, the rate of evaporation slows down. This is because air has enough moisture and cannot hold more moisture.
Thus, the statement ‘increases in relative humidity decreases the rate of evaporation of water’ is correct.

The velocity of sound is affected by temperature and relative humidity. The density of moist air is less than that of dry air. Thus, the velocity of sound in moist air is greater than that in dry air.
Thus, the statement ‘increases in relative humidity increases the velocity of sound’ is correct.
Thus, the correct statements are (I), (II) and (IV).

Thus, the correct options are (I), (II) and (IV).

Note:The velocity of sound is affected by temperature and relative humidity. The density of moist air is less than that of dry air. As moist air is less dense sound can easily pass through it. Thus, as the relative humidity increases, the velocity of sound in air increases.