know about Air

Hi folks,
Air is a mixture of gases. That means there are many gases mixed in air. You know about one already. It is water vapour, the gaseous form of water. How can you be sure that there is water vapour in air?
Put some ice or very cold water in a glass. Place the table. Soon you will see drops of water outside the glass. Where does the come from? The water vapours in the air cools when it comes near the glass and change in to water. There are many other gases in air. Oxygen, nitrogen and carbon dioxide are three of them. Of these, oxygen is the most important to us. We need to live. Thank you.