Explanation

The pressure of oxygen in the lungs is 104 torr. 

The partial pressure of oxygen in the lungs, also known as the alveolar partial pressure of oxygen (PaO2),

It is the pressure exerted by oxygen within the alveoli.

At sea level, atmospheric pressure is 760 mmHg.

Since oxygen makes up approximately 21% of air,

The partial pressure of oxygen in atmospheric air is 0.21 x 760 mmHg = 159.6 torr

However, as air enters the alveoli, it mixes with water vapor and carbon dioxide, which slightly reduces the oxygen partial pressure.

Therefore, the actual partial pressure of oxygen in the alveoli is around 104 torr.