What percentage of atmospheric air is composed of O2?

Atmospheric air is primarily composed of nitrogen and oxygen, with oxygen making up a significant portion of the atmosphere. The commonly accepted concentration of oxygen in the atmosphere is approximately 20.8%. This value represents the typical percentage of oxygen present at sea level in the Earth's atmosphere, which is essential for sustaining life and is a critical factor in various physiological processes.

Understanding this percentage is important for fields such as medicine, where oxygen levels influence respiratory function, and in various industrial applications where oxygen availability affects combustion processes. The values presented in the other options do not align with the scientifically established percentage of oxygen in the atmosphere, thus reaffirming that 20.8% is the most accurate representation of O2 content.