Correct option is (c) Coal gas
The best I can explain: Coal gas is called as town gas. It is a by-product obtained during destructive distillation of coal. It mainly contains H2, CO, CO2, CH4 and N2. It has a calorific value ranging from 21000KJ/m^3 to 25000KJ/m^3. The gas obtained when coal is heated strongly in the absence of air is called coal gas.