What is special about nitrogen and what is its function in the atmosphere

Nitrogen makes up 70-80% of the atmosphere. If nitrogen weren't here, we wouldn't be able to breathe in oxygen because of the density of the air and because the air would then be toxic and flammable because there would be too much oxygen in the air. So with nitrogen, we are able to breathe safely. It makes it so we can breathe and keeps the atmosphere at a normal density.
Hope this helps. 

It shows that the experiment is designed properly.