Question

Why do we say we are breathing in oxygen when the atmosphere consists of Nitrogen — 78 percent Oxygen — 21 percent?

Answer 1

Because we cannot breathe nitrogen!

Explanation:

Our human body needs oxygen to make `ATP`, so that's why we say that we are breathing oxygen instead of nitrogen. Even though nitrogen is abundant in more than `3` times the amount of oxygen in the atmosphere, we cannot breathe it in our body, so we say that we breathe oxygen, as that's element that we need to make `ATP` for our body to use.