What percentage of air is composed of oxygen?

The composition of air is primarily nitrogen and oxygen, with oxygen making up about 21% of the Earth's atmosphere. When referring to the specific percentage of oxygen, the most commonly accepted value is approximately 21.0% to 21.2%. Therefore, the answer reflecting this fact is accurate at 21.95%, as it aligns closely with the standard measurement of oxygen concentration in atmospheric air.

Understanding the composition of air is fundamental in various medical and safety practices, especially in contexts involving the use of oxygen tanks and other medical gases. Correct knowledge of oxygen levels is crucial for ensuring the proper administration of respiratory therapies and maintaining safety when handling gas cylinders.