what is oxygen and air different?

Oxygen is a pure gas with chemical formula O₂.

Air is a gaseous mixture containing about 80% of nitrogen gas (N₂), 20% of oxygen gas (O₂) and small amounts of carbon dioxide (CO₂), water vapor (H₂O) and noble gases.

Oxygen gas, O2, which is one of many ways that oxygen can exist in nature, is only about 20 % of the mass of air. Almost all of the rest is nitrogen gas (N2). Our air is actually nitrogen gas with some oxygen, not the other way around. We can't use nitrogen gas for our internal chemistry though. We need oxygen gas instead.

Most of oxygen on earth has already reacted with other elements and formed oxide compounds. Those aren't very helpful for our body chemistry. Carbon dioxide gas is probably the most important oxide gas in the air in terms of concentration (and it is mostly what our body makes when it uses O2 gas from air). Most oxygen exists in rock, primarily as silicate (SiO2, SiO3, SiO4) compounds. Lots of oxygen but most of it is no good for our needs. Thank god for plants making O2 gas.

Oxygen is a component of air.

oxygen is an element and it is pure while air is a mixture of many gasses.