Which of the following has the highest calorific value?

The amount of energy produced by the complete combustion of a material or fuel is called calorific value.

Hydrogen has a high calorific value of 1,50,000 kJ/kg. It is because hydrogen is highly combustible and it reacts explosively and produces a very high amount of energy when it comes in contact with air.

Methane, CNG, and LPG do not produce that amount of energy when it comes in contact with air so the calorific value is lesser as compared to hydrogen. Due to its high calorific value, hydrogen is used as rocket fuel.