Final answer:
The correct partial pressure of oxygen in the alveoli is 104 mm Hg, which allows for a strong pressure gradient facilitating gas exchange with the blood in the pulmonary capillaries.
Step-by-step explanation:
The partial pressure of oxygen in the alveoli is a measure of the amount of gaseous oxygen available for gas exchange in the lungs. The correct answer to the question is (b) 104 mm Hg. This is because oxygen has a high partial pressure in the alveoli, about 104 mm Hg, which creates a strong gradient for oxygen to rapidly diffuse into the blood of the pulmonary capillaries, where its partial pressure is about 40 mm Hg. This gradient is crucial for efficient gas exchange during respiration.