Final answer:
Expired air contains approximately 16% oxygen, as the body has used some of the oxygen inhaled for metabolic processes and has produced carbon dioxide.
Step-by-step explanation:
The question is asking about the amount of oxygen contained in expired air after a person exhales. Inhaled air contains approximately 20.9% oxygen, which is used for metabolic reactions in the body that produce ATP and CO₂ as a by-product. When we exhale, the concentration of oxygen is reduced because some has been absorbed by the body for these reactions. The expired air typically contains approximately 16% oxygen as the body has used a portion of the oxygen and produced carbon dioxide as a waste product, which is also expelled.