Here's why:

* Elements are the simplest pure substances that cannot be broken down into simpler substances by ordinary chemical means. They are found on the periodic table.

* Compounds are formed when two or more different elements combine chemically in a fixed ratio.

* Mixtures are combinations of two or more substances that are not chemically bonded and can be separated by physical means.

Nitrogen (N) is a pure substance found on the periodic table and cannot be broken down into simpler substances.