Here's why:

* Elements are the simplest pure substances that cannot be broken down into simpler substances by chemical means. They are made up of only one type of atom.

* Oxygen is a chemical element with the symbol O and atomic number 8.

* Nitrogen is a chemical element with the symbol N and atomic number 7.

* Hydrogen is a chemical element with the symbol H and atomic number 1.

These elements are fundamental building blocks of matter and are found in countless compounds and molecules.