The process of separation of different constituents from petroleum is called refining.
The petroleum gas, petrol, diesel, kerosene, paraffin wax, lubricating oil are obtained by this process. It is carried out in a petroleum refinery.
(c)
The least polluting fuel for vehicles is CNG (Compressed Natural Gas).
It is a very important fossil fuel because it is easy to transport, and it creates less smoke and pollution.