The correct choice is (c) Mond gas
Easy explanation: Mond gas is gaseous fuel that is produced by passing air and large amount of steam over waste coal at about 650^oC. It has a calorific value of 5800KJ/mm^3. The mond gas process was designed to convert cheap coal into flammable gas, which was made up of mainly hydrogen while recovering ammonium sulphate. The gas produced was rich in hydrogen and poor in carbon monoxide. Although it could be used for some industrial purposes and power generation, the gas was limited for heating or lighting.