CBSE Class 8 Answered

Crude petroleum must be refinned before it is used as a fuel or other purposes .

It is a mixture of various constituents like petroleum gas , parafin wax, petrol,diesal,lubricating oil etc.

The basic step in the refinning process is distillation .

Distillation is seperates crude oil into a variety of groups by boiling them until they vapourise.

The vapour is allowed to cool at different temperatures in a huge tower .

At each temperature , a number of hydrocarbons become liquid and seperste out .

These are called fractions .

Hence, this process is known as fractional distillation .