Which of the following is the best fuel in terms of energy released per gram of fuel?

The amount of energy released increases with the number of bonds present in the chemical substance or fuel. That is because each bond has a certain amount of energy stored in it therefore the more bonds the more energy is stored and more energy is released if these bonds break through combustion. Theoretical values of energy released per gram of fuel (in joules/ gram) are: Hydrogen: 142.5 KJ/g; Methane: 55.6 KJ/ g; Ethanol: 29.7 KJ/g; Butane: 49.6KJ/g.