Question

How to show the air contain water vapour?

Answer 1

Just take a cold glass of water and place it anywhere for a while. You will see drop of water outside the glass. As the water vapors in the air strike the cold glass, they loose their kinetic energy and condense on the outer surface. That's why you see the water outside glass.

Answer 2

simple take a glass fully filled with cold water and keep it outside u can see the some droplets this shows u air contain water vapour