Why doesn't hydrogen have twice the lift as helium?

Question

Why doesn't hydrogen have twice the lift as helium?

Answer 1

Because the lift is not a direct effect of the weight of the hydrogen or helium gas, but of the difference of the weight of the helium or hydrogen has with air.

Air weights about 29 g per "mole" (equivalent, since air is not a pure gas). Helium weights 4 g per mole (around 24 l at room temperature) so its buoyancy is (29-4) 25 g per mole; while hydrogen is (29-2) 27 g per mole, a mere 8% improvement.