The calorific values of three fuels A, B and C are 33 kj/g, 48 kj/g and 150 kj/g, respectively. A is solid, B is liquid and C is a gas at room temperature. On combustion, both A and B produce carbon dioxide while C explodes forming steam. B and C leave no residue after combustion while A leaves behind some solid residue. Which one of the three fuels is the most ideal? Give two reasons to support your answer.