Air is the Earth's atmosphere. It is the clear gas in which living things live and breathe. It has an indefinite shape and volume. It has no color or smell. It has mass and weight. It is a matter as it has mass and weight. Air creates atmosphere pressure. There is no air in the vacuum and cosmos.
Air is a mixture of 78.03% nitrogen, 20.99% oxygen, 0.94% argon, 0.03% carbon dioxide, 0.01% hydrogen, 0.00123% Neon, 0.0004% helium, 0.00005% krypton and 0.000006% xenon. There are also small amouts of other things.
Animals and humans need the oxygen in the air to live. In the human body, the lungs give oxygen to the blood, and give back carbon dioxide to the air. Plants need the carbon dioxide in the air to live. They give off oxygen that humans can breathe again.