The correct answer is: A. hydrogen
Hydrogen has the highest energy value (calorific value) of all the gases listed. It has a calorific value of 120 MJ/kg, which is significantly higher than the calorific values of LPG (46 MJ/kg), natural gas (39 MJ/kg), and methane (50 MJ/kg).
LPG is a mixture of propane and butane, which are both hydrocarbons. Natural gas is a mixture of methane, ethane, propane, and butane. Methane is the simplest hydrocarbon and has the lowest energy value of all the gases listed.
The energy value of a fuel is the amount of heat that is released when the fuel is burned. The higher the energy value of a fuel, the more heat is released when it is burned. This means that hydrogen can produce more heat than any of the other gases listed when it is burned.
Hydrogen is a clean-burning fuel that does not produce any harmful emissions. It is also a renewable resource, which means that it can be produced from water. This makes hydrogen a promising alternative to fossil fuels, which are non-renewable and produce harmful emissions.