What is the oxygen percentage in air?

The oxygen percentage in air is approximately 21%. This percentage is consistent across the Earth's atmosphere at sea level and is a crucial component of air composition. Understanding the percentage of oxygen in air is important in scuba diving, particularly when discussing gas mixtures and the potential implications for diving with enriched air nitrox.

In scuba diving, especially when using nitrox, divers must be aware of the oxygen content because increased oxygen levels can lead to oxygen toxicity at greater depths. This is why the baseline percentage of oxygen in regular air is such an essential reference point for divers.

The other options suggest lower or higher oxygen concentrations, which do not accurately reflect the composition of the atmosphere. Recognizing the correct percentage helps divers make informed decisions regarding dive planning, gas mixtures, and safety.