Scuba Diving International (SDI) Computer Nitrox Practice Exam

The air we normally breathe consists primarily of which gases?

1. Hydrogen and Helium

2. Nitrogen and Oxygen

3. Carbon Dioxide and Nitrogen

4. Oxygen and Argon

The correct answer is: Nitrogen and Oxygen

The air we normally breathe consists primarily of nitrogen and oxygen. In the atmosphere, nitrogen makes up about 78% of the air, while oxygen constitutes approximately 21%. This balance is essential for supporting life on Earth, as oxygen is crucial for respiration in most living organisms. The presence of nitrogen, although it does not participate in respiration, plays a vital role in diluting the oxygen and preventing it from being toxic at higher concentrations. The other gases present in the atmosphere, such as argon, carbon dioxide, and trace gases, are minimal in comparison and do not significantly alter the composition of the air we breathe. Understanding the composition of breathable air is essential for divers, particularly when using different gas mixtures for diving, such as nitrox, which alters this balance to optimize oxygen levels while minimizing the risks associated with higher nitrogen levels.