Question

How can you show that air contains water vapour

Answer 1

Air contains water vapour..

Let see how

Take a bottle containing cold water out in the hot. after some time you will notice droplets of water around it.
the cold surface of the bottle condenses the water vapour present around it into water droplets. this activity proves that air contains water vapour.

Answer 2

put some ice peace in half filled water glass of
steel
after some time you will see that water have deposited outside of glass