The partial pressure of oxygen (pO2) in the alveoli is approximately:

 # The partial pressure of oxygen (pO2) in the alveoli is approximately:

A. 40 mm Hg

B. 160 mm Hg

C. 104 mm Hg

D. 95 mm Hg

The correct answer is C. 104 mm Hg.

The partial pressure of oxygen (pO₂) in the alveoli is approximately 104 mm Hg under normal conditions. This value is calculated based on the atmospheric pressure (760 mm Hg at sea level), the fraction of oxygen in inspired air (about 21%), and adjustments for water vapor pressure (47 mm Hg at body temperature) and the effects of carbon dioxide and nitrogen in the alveoli. The alveolar pO₂ is lower than the atmospheric pO₂ (about 160 mm Hg) due to these factors.