Fractional distillation works on the principle of: 

The separation of two or more liquids that mix well via fractional distillation. It involves a unique kind of distillation. The liquid combination is heated during the procedure. In order to achieve a vapour pressure equivalent to atmospheric pressure escape from the combination, the liquid boils when heated and transforms into vapours. The purified component is then obtained by condensing these vapours.

Distillation includes fractional distillation. Miscible liquids must be separated during the procedure. The combination is first distilled, and then it is separated into its individual components by condensation. When the liquid combination is heated to entrain temperature, the separation occurs. The fractions of the mixture begin to evaporate at a specific temperature.

The fundamental idea behind fractional distillation is that different liquids have distinct boiling points and boil at those points at various temperatures. The temperature at which a liquid's vapour pressure reaches equilibrium with air pressure is known as the boiling point. Low boiling point substances need less heat to vaporise than high boiling point substances. The mixture is readily breached by this component, and the condenser condenses the vapour.

Fractional distillation works on the principle of varying boiling points.

Hence, the correct answer is A.