Unbreathed air mainly contains what?

By "unbreathed" I assume you mean the air that is present in our atmosphere and around us.
The air (or unbreathed air) is composed of a number of gases. The chief among them is nitrogen (chemical symbol: N) and accounts for about 78% of the volume of air. The next major constituent is oxygen (chemical symbol: O). Oxygen accounts for about 21% of the volume of air. Oxygen is also critical for the survival of living beings (aerobic life forms only) on Earth. We as humans cannot survive without regular intake of oxygen.
Argon (chemical symbol: Ar) accounts for about 1% of the volume of air. Carbon dioxide (chemical formula: CO2) accounts for about 0.04% of air, by volume. There are other constituents of air as well, including water vapors and minor (or trace) concentrations of other gases, such as hydrogen, helium, methane, and so on.
Hope this helps.