What percentage of oxygen is present in the air that enters the lungs?

The correct percentage of oxygen present in the air that enters the lungs is around 20.9%. This figure is based on the composition of the Earth's atmosphere, where oxygen makes up approximately 20.9% of the air by volume. This value is important for understanding respiratory physiology and how oxygen is delivered to the body's tissues.

Oxygen in the air is crucial for cellular respiration, a process that produces energy in our cells. The lungs facilitate the exchange of gases, allowing oxygen to enter the bloodstream while carbon dioxide is expelled. Knowing the accurate percentage helps in assessing respiratory function and understanding the importance of oxygen levels in various environments.

While other percentages listed may seem plausible, they do not accurately reflect the standard composition of atmospheric air. This knowledge is fundamental for anyone involved in first aid or healthcare, as it underlines the necessity of providing adequate oxygenation in emergency situations.