Fractional distillation is based on the property that:
A) Density of each fraction is different.
B) Molecular weight of each fraction is different.
C) Boiling point of each fraction is different.
D) Melting point of each fraction is different.

Hint: We know that the technique used in purification of liquids or for the separation of liquid components from a mixture is known as fractional distillation. In the process of fractional distillation, the liquid is heated to its boiling point and converted to vapour. The vapours are again condensed to liquid.

Complete step by step answer:
In the process of fractional distillation, a mixture of different substances having different boiling points is heated in a fractional column.
Fractional distillation separates components of a mixture into a number of fractions in an increasing order of their boiling points.
In the process of fractional distillation, vapours from the boiling solution pass along a column.
The temperature of the fractional column decreases along its length. The components that have high boiling points undergo condensation on the column and return to the solution. The components that have low boiling points pass through the column and get collected.
The fractional distillation process is generally used for the refining of crude petroleum.
In simple words, fractional distillation is the process of separation of a mixture into fractions by their boiling points by heating them to a temperature at which one or more fractions vaporize.
Thus, fractional distillation is based on the property that the boiling point of each fraction is different.

Thus, the correct option is (C) boiling point of each fraction is different.

Note: Fractional distillation is used for the components that do not have wide differences in their boiling points. For the components that have significant differences in their boiling points simple distillation is used. Simple distillation is used when small impurities are present in the liquids.