Oxygen is a gas on the periodic table. It is represented by the symbol O and the atomic number 8. It is an important component of the air that you breathe. It makes up about 21% of air. Too much or too little oxygen can cause you serious harm.
Nitrogen is a gas that makes up about 78% of air. It is represented by the symbol N and the atomic number 7. It is a component of all living organisms. However, in its pure form, it has no vital use for humans above water. Underwater, nitrogen needs to be carefully tracked. Nitrogen needs to be released from the body slowly. If not, it can lead to decompression problems.
Many other gases make up the remaining 1% of air. A few of them are argon, carbon dioxide, helium, hydrogen, methane, and neon. Except for carbon dioxide, most of these gases have no effect when underwater.