Why won't you try and see?

They will not eat anything that's not good for them.

Air is a mixture of different molecules. On average the composition is:

78% Nitrogen in gas form (N₂)
21% Oxygen (O₂)
0,9% Argon (Ar)
0,1% Carbon dioxide (CO₂)

There is ofcourse more gases but the percentage is so small.

Xenon (Xe) for example is at 0,09 million percent.