Exhaled air contains approximately which composition?

Exhaled air contains approximately which composition?

• A. 16% oxygen and 3% to 5% carbon dioxide
• B. 21% oxygen and 0.04% carbon dioxide
• C. 10% oxygen and 10% carbon dioxide
• D. 0% oxygen and 0% carbon dioxide

Answer: (A)

Gas exchange in the lungs shifts the composition of the air we exhale: oxygen is used by the body's tissues, and carbon dioxide produced by metabolism is expelled. Inhaled air starts with about 21% oxygen and only trace CO2 (around 0.04%). After passing through the lungs, exhaled air typically contains about 16% oxygen and roughly 3–5% carbon dioxide, with the rest largely nitrogen and water vapor. This is why the described exhaled-air composition is right: it matches the typical levels after gas exchange. The other numbers correspond to inspired air, unusually high or low CO2 values, or impossible extremes for normal breathing, not to normal exhaled breath.

Gas exchange in the lungs shifts the composition of the air we exhale: oxygen is used by the body's tissues, and carbon dioxide produced by metabolism is expelled. Inhaled air starts with about 21% oxygen and only trace CO2 (around 0.04%). After passing through the lungs, exhaled air typically contains about 16% oxygen and roughly 3–5% carbon dioxide, with the rest largely nitrogen and water vapor.

This is why the described exhaled-air composition is right: it matches the typical levels after gas exchange. The other numbers correspond to inspired air, unusually high or low CO2 values, or impossible extremes for normal breathing, not to normal exhaled breath.