Explanation:

Coal gas contains a variety of calorific gases including hydrogen, carbon monoxide, methane and volatile hydrocarbons together with small quantities of non-calorific gases such as carbon dioxide and nitrogen.
Coal gas is a flammable gaseous fuel made from coal and supplied to the user via a piped distribution system.
The gas obtained when coal is heated strongly in the absence of air is called coal gas.
Coal gasification is the process of producing syngas–a mixture consisting primarily of carbon monoxide (CO), hydrogen (H2), carbon dioxide (CO2), methane (CH4), and water vapour (H2O)–from coal and water, air and/or oxygen.