pO2 among the following is least inAlveoliOxygenated bloodDeoxygenated bloodAtmospheric air

The pO2, or partial pressure of oxygen, is least in deoxygenated blood. Here's why:

1. Atmospheric air: The pO2 in atmospheric air is the highest among the options, typically around 159 mmHg at sea level.

2. Alveoli: The pO2 in the alveoli is slightly lower than atmospheric air due to the mixing of inhaled air with the residual volume of the lungs. It's typically around 104 mmHg.

3. Oxygenated blood: The pO2 in oxygenated blood is slightly lower than in the alveoli, as some oxygen is taken up by the blood cells. It's typically around 95-100 mmHg.

4. Deoxygenated blood: The pO2 in deoxygenated blood is the lowest among the options, as most of the oxygen has been used up by the body's tissues. It's typically around 40 mmHg.