The constant temperature at which a pure liquid is completely transformed into its vapour under normal atmospheric pressure is called its boiling point and this phenomenon is called boiling.
In other words, boiling point is that constant temperature at which the vapour pressure of a liquid is exactly equal to the atmospheric pressure.
A pure liquid has a constant boiling point at a constant pressure, which is a characteristic property of the liquid. Impure liquids boil at a higher temperature than the pure liquid.
Hence, the determination of this physical constant not only helps in judging the purity of the liquid, but also to a certain extent in the identification of a liquid sample.
Changing of gaseous state to liquid state (condensation)
Condensation is the change of water from its gaseous form (water vapour) into liquid water. Condensation generally occurs in the atmosphere when warm air raises, cools and loses its capacity to hold water vapour. As a result, excess water vapour condenses to form cloud droplets.