Q$.$How can hydrogen have high gravimetric energy density but low volumetric density $($ I know what they mean $,$ I mean it's contradictory$)$ how can something have high weight but less Volume at same time

Plz explain this in a intuitive way maybe using an simple analogy

Q$.$ Also what is the reason hydrogen has high gravimetric energy density $($ I mean scientifically or at an atomic level$)$