Which one of the following energy sources has the lowest energy content per unit mass?

Biomass has the lowest energy content per unit mass among these fuels.

Coal packs far more energy per kilogram than biomass.

Hydrogen holds the highest energy per unit mass of any common fuel.

Natural gas also carries much more energy per kilogram than biomass.

Biomass includes wood, crop residue and dung, all with high moisture and ash.

This moisture and low carbon density lower its energy yield.