1st, Helium is a rare gas (Group 0 element). As such, it is very stable and exist
as its own as a Monatomic Element. It is NOT A DIATOMIC MOLECULE.

Thus, we will have:
Mass of He
= mol X atomic mass
= 0.5 X 4
= 2.0 g

0.5mol of Helium is heavier than 1g of Gold.

Hope this is clear to you.

Helium is diatomic.

Mass of He
= mol X molar mass
= 0.5 X 8
= 4.0 g

hence, He has a greater mass than 1g of Gold?

Kindly correct me if I am wrong.
Thank you.