Concept:A vapour is a gaseous substance that exists below its critical temperature, so it can return to its liquid state easily, whereas a true gas cannot be readily condensed by pressure alone.
Explanation:A gas is permanently in the gaseous state at ordinary temperature and cannot be liquefied by pressure alone.
A vapour, on the other hand, is the gaseous form of a substance that is normally a liquid or solid at room temperature.
Because a vapour is in equilibrium with its liquid (below the critical temperature), it easily condenses back into a liquid when pressure is applied or temperature is lowered.
Therefore, the key difference is that vapour can be easily condensed into a liquid, while gases are harder to liquefy under ordinary conditions.
Answer:B. Unlike gases, vapour can easily be condensed into liquids.