Question

Which one of the following gases is lighter than air?

Options

• Carbon dioxide

• Chlorine

• Oxygen

• Hydrogen

Answer 1

Hydrogen

Explanation:

Hydrogen (density 0.090 g/L at STP, average molecular mass 2.016 g/mol) and helium (density 0.179 g/L at  STP, average molecular mass 4.003 g/mol) is the most commonly used lift gases. Although helium is twice as heavy as (diatomic) hydrogen, they are both so much lighter than air that this difference only results in hydrogen having 8% more buoyancy than helium.