## Core Concept
The normal range of hemoglobin O2 saturation in systemic venous blood is approximately 75% to 80%, reflecting the body's oxygen extraction. In systemic arterial blood, the saturation is around 95% to 100% under normal conditions. This difference is crucial for understanding oxygen delivery and utilization.

## Why the Correct Answer is Right
The correct range from systemic venous to systemic arterial blood representing a normal resting condition is **75% to 95%**. This range accurately reflects the body's normal oxygen extraction ratio and the efficient oxygenation of blood in the lungs. At rest, the body extracts about 25% of the oxygen from the arterial blood as it passes through the tissues, resulting in a venous oxygen saturation of approximately 75%. The arterial oxygen saturation is around 95% due to the high efficiency of gas exchange in the lungs.

## Why Each Wrong Option is Incorrect
- **Option A:** This range is too low for both venous and arterial values under normal conditions.
- **Option B:** This range starts at a slightly higher venous saturation than expected but still within a plausible range; however, it does not accurately represent the typical arterial saturation range.
- **Option C:** This option suggests a very narrow and high range that does not accurately reflect the normal physiological difference between venous and arterial oxygen saturation.

## Clinical Pearl / High-Yield Fact
A key point to remember is that a normal arterial oxygen saturation (SpO2) is >95% on room air at sea level. Venous oxygen saturation (SvO2) being around 75% indicates adequate oxygen extraction by tissues. Abnormal values can indicate issues such as hypoxemia, anemia, or significant tissue hypoxia.

## Correct Answer: .