Question

The vapour pressure of a liquid at its boiling point is equal to
A.) $1atm$
B.) $2atm$
C.) $3atm$
D.) $4atm$

Answer 1

As we know that the boiling point of a substance or of a liquid is that temperature at which the vapour pressure of that liquid becomes equal to the pressure surrounding the substance or the liquid.

Complete step by step answer:
As we know that whenever a liquid is heated then the molecules of liquid get sufficient energy that is kinetic energy to overcome the forces that hold them in a liquid. Therefore, the molecules of liquid gas escape into the gas phase. Then these molecules in the gas or vapor phase that are present above the liquid creates a pressure. This pressure is known as vapor pressure.
Also, we know that the boiling point of a liquid is that temperature at which the vapour pressure of that liquid becomes equal to the surrounding pressure or the atmospheric pressure in normal conditions. At the boiling point of the liquid the pressure of the liquid is atmospheric pressure. Therefore, the vapour pressure of a liquid at its boiling point will be equal to the atmospheric pressure. As we know that the atmospheric pressure is $1atm$.
Therefore, the vapour pressure of a liquid at its boiling point will be equal to $1atm$.

Hence, option A is the correct answer.

Note: Remember that if the surrounding pressure of a liquid is one then the liquid boils at its normal boiling point but if the surrounding pressure of the liquid is higher than one atmosphere, then the liquid will boil at a higher temperature than that of normal boiling point and if the surrounding pressure of the liquid is lower than one atmosphere, then the liquid will boil at a lower temperature than that of normal boiling point