Answer: Hydrogen molecule is lighter in weight than molecules of Oxygen and Nitrogen.
Explanation:The lighter the weight of a gaseous molecule the easier for it to float and overcome the Earth's Gravitational force or pull. Hydrogen molecule is able to escape the Earth's Gravitational pull because of its light or low molecular weight, while Oxygen and Nitrogen are heavier hence they are trapped and prevented from escaping from the Earth's Gravitational pull.
Hydrogen gas molecular weight=2.016g/mol
Oxygen gas molecular weight=16g/mol
Nitrogen molecular weight=28.018g/mol.