Which of the following gases has the highest calorific value?

Hydrogen has the highest calorific value of these gases, releasing the most heat per unit mass.

Butane yields good heat but far less per kilogram than hydrogen.

Methane has a high calorific value yet still below hydrogen.

Ethane too falls short of hydrogen's heat output.

Hydrogen's energy is released as it forms water on burning, with no carbon.

This makes hydrogen attractive as a clean future fuel.