If air is mostly nitrogen and about 20% oxygen, then...?

Question

where does all this nitrogen go when we breathe in air? and why do people answer "oxygen" to the question "what do we breathe in?" shouldn't it be nitrogen? or is it because oxygen is the valuable gas that our bodies need?

Answer 1

remember that we breathe air. Air is a mixture of a lot of stuff ...mostly N and O Scuba divers breathe air also...The bends is when dissolved nit in the blood stream returns to its gaseous form...therefore we absorb some nitrogen....the rest is exhaled

Answer 2

Nitrogen is almost completely inactive.  When we breathe in  we keep some of the oxygen, it goes into our bloodstream.  We breathe out a little bit of carbon dioxide.  But the nitrogen just goes in and comes back out, we don't use it for anything.

Our bodies are designed to live in a 20% oxygen atmosphere.  If it was 20% oxygen and 80% neon or xenon it would be the same.  If the atmosphere was more than 20% oxygen, fires would start much more easily.