Question

What is the difference between gas and vapour?

Answer 1

Vapour can be called as a gas but a gas is not a vapour. In simple terms, vapour is formed by converting either a solid to gas (sublimation) or a liquid to gas (boiling).
Vapour actually consists of phase change with equilibrium between two phases. Gas itself is a phase of matter. Vapour can be converted back to the solid or liquid form. Gas needs special treatment to convert to liquid or solid form.