Helium and Hydrogen lifting abillity

good explanation !!!

But none of this explains the buoyancy power of fizzy lifting drinks!!!

also Hydrogen is not found in the usual state we get from a tank of it. Hydrogen is a double molecule H2,

don'rt ask me why,

Yet, remember that atomic mass has nothing to do with weight, which is based on density, which is determined how the atoms pack together.

There are a number of incidence on the elemental chart where the atomic mass of one element is greater than another element, but a cm³ of the element with higher atomic mass is not as heavy as the element with lower atomic mass. It all depends on how many atoms of an element can be packed into that cm³.

True for solids and liquids. However, for gases, the density is directly proportional to the molecular weight, with a small error to account for the non-ideal nature of the gas.

Tad

Yet, remember that atomic mass has nothing to do with weight, which is based on density, which is determined how the atoms pack together.

In liquids and solids, that is correct, sort of. Actually, the weight (mass) of a mole's worth of a solid is directly related to atomic mass. The volume occupied by a solid depends on its density, which depends on the factor you mention.

For gases, this is not true, and you can compare the densities of gases just by comparing their molecular weights (with a couple caveats).

Would surpose that because hydrogen as a gas is h2 a diatomic molecule the relative density of the diatomic molecule would de greater than its components where as helium is inert and exists as lone atoms with atomic weight 2 / but thats just a guess

That's a very reasonable guess, but in gases, the density is directly related to to the molecular weight (with just slight imperfections in the relationship).