Question

What does partial pressure of oxygen mean?

Answer 1

The partial pressure of any gas in a gaseous mixture is the same as the pressure that gas would exert if it alone occupied the container.

Explanation:

Both you and I are currently breathing air at approx. `1*atm` pressure. In terms of partial pressures, this is `0.21*atm` `"dioxygen"`, and `0.79*atm` `"dinitrogen"`. The total pressure is the sum of the partial pressures.