(a) Fossil fuels are coal , petroleum and natural gas.
(b) Process of separation of different constituents from petroleum is called refining.
(c) Least polluting fuel for a vehicle is compressed natural gas.
(a) Fossil fuels are hydrocarbons that includes coal, petroleum and natural gas. A fossil fuel is formed by anaerobic decomposition of buried dead organisms containing organic molecules.
(b) Petroleum refining processes are the chemical engineering processes used in petroleum refineries to transform crude oil into useful products such as liquefied petroleum gas, gasoline or petrol, kerosene, jet fuel, diesel oil and fuel oils.
(c) Compressed natural gas or CNG is a type of natural gas which is mainly composed of methane that is stored under high pressure in its gaseous form to transport it or for storage.