Answer 1 .
Oxygen [O 2 ] is a chemical element which exists at normal temperatures and pressures as a colorless, odorless, and tasteless gas..
It combines with many other …elements, creating "oxides" of those elements. It is a component in the mixture we call Air..
Answer 2 .
For humans O 2 in the air is used for breathing, and O 3 [Ozone] is for protecting us from the harmful Ultraviolet radiation from the Sun. ( Full Answer )