What is the percentage of oxygen in expired air when a person is resting?

There are 21% of oxygen that contain in expired air.

To determine the percentage of oxygen in expired air when a person is resting, we need to consider the composition of air and the process of respiration.

Air is composed of approximately 21% oxygen, 78% nitrogen, and small amounts of other gases such as carbon dioxide and argon.

During respiration, inhaled air moves into the lungs where gas exchange takes place. Oxygen from the inhaled air is absorbed by the blood and transported throughout the body, while carbon dioxide, a waste product, is expelled from the body through exhalation.

When a person is at rest, the respiratory rate is relatively stable, and the oxygen consumption matches the body's metabolic needs. At rest, the average percentage of oxygen in expired air is around 16-17%.

To accurately measure the percentage of oxygen in expired air of an individual resting, specialized equipment such as a spirometer or gas analyzer is required. These devices can provide precise measurements of the composition of expired air and other respiratory parameters.