Why human use oxygen to breath not nitrogen?

Question

Why human use oxygen to breath not nitrogen?

Answer 1

Nitrogen gas (N2) has a triple bond which is much harder to break than oxygen's double bond (O2).  Some bacteria can break this bond and thus allow plants to use the nitrogen from the air, but most organisms cannot do this.

Answer 2

Because either we evolved that way, or God created us that way.

But oxygen is the heavier gas and is closer to the Earth in much bigger amounts; so we use Oxygen and not Nitrogen.