What is special about nitrogen?
and what is it main function?

Nitrogen is present in many spheres of the Earth, including the atmosphere and biosphere. Nitrogen makes up around 80% of the atmosphere (more than oxygen), and exists as a diatomic molecule.  it's also essential in the function of plants, as the most commonly used mineral nutrient. It is also used in photosynthesis and is a major component of amino acids which make protein. 

The gas would begin to expand, and eventually the can would burst or explode.