Question

Explain that exhaled air contains water vapour?

Answer 1

inhaled air contains water vapour because there is water vapour present in the air in the form of humidity or moisture.

Answer 2

Air is a mixture of many substances and gases. It contains nitrogen, co2, oxygen and even water vapours.
There is no doubt why air contains vapours of water. This is universal for every planet which has watery oceans on it and thrives life.