## **Core Concept**
The partial pressure of oxygen (pO2) at atmospheric pressure can be calculated using Dalton's Law of Partial Pressures. At sea level, atmospheric pressure is approximately 760 mmHg, and dry air is composed of 21% oxygen.

## **Why the Correct Answer is Right**
To calculate the partial pressure of oxygen (pO2) at atmospheric pressure (760 mmHg), we use the formula: pO2 = (atmospheric pressure - water vapor pressure) * FiO2, where FiO2 is the fraction of inspired oxygen (approximately 0.21 or 21% at sea level). The water vapor pressure at 37°C (body temperature) is about 47 mmHg. Therefore, pO2 = (760 - 47) * 0.21.

## **Calculation:**
pO2 = 713 * 0.21 = 149.73 mmHg, which is approximately 150 mmHg.

## **Why Each Wrong Option is Incorrect**
- **Option A:** This option is incorrect because it does not match the calculated value of pO2 at sea level.
- **Option B:** This option suggests a value that is not consistent with the standard calculation for pO2 at atmospheric pressure.
- **Option D:** This option is incorrect as it suggests a much lower partial pressure of oxygen than what is expected at sea level.

## **Clinical Pearl / High-Yield Fact**
A key point to remember is that the partial pressure of oxygen in arterial blood (PaO2) is normally around 75-100 mmHg in healthy individuals breathing room air at sea level. However, the question specifically asks about the partial pressure of O2 at atmospheric pressure without considering the effects of water vapor pressure and the specific conditions of the lungs or blood.

## **Correct Answer:** . 160 mm Hg