**Core Concept**
The question is testing the concept of oxygen hemoglobin dissociation curve and the effect of varying oxygen concentrations on the partial pressure of oxygen (pO2) in arterial blood.

**Why the Correct Answer is Right**
When 100% oxygen is administered under atmospheric pressure, the partial pressure of oxygen in arterial blood (pO2) will increase. However, the body's tissues and organs have a limited capacity to utilize oxygen, and the oxygen hemoglobin dissociation curve shows that the binding of oxygen to hemoglobin is not directly proportional to the partial pressure of oxygen. In other words, the blood can only carry a certain amount of oxygen, regardless of the partial pressure. This is known as the "loading curve" of the oxygen-hemoglobin dissociation curve. At 100% oxygen, the partial pressure of oxygen in arterial blood will be approximately 760 mmHg, but the oxygen saturation of hemoglobin (SaO2) will be around 98-99% due to the limited capacity of hemoglobin to bind oxygen.

**Why Each Wrong Option is Incorrect**
* **Option A:** There is no direct correlation between the partial pressure of oxygen and the oxygen saturation of hemoglobin at high oxygen concentrations.
* **Option B:** The partial pressure of oxygen in arterial blood at 100% oxygen is not directly related to the partial pressure of carbon dioxide (pCO2).
* **Option C:** The Bohr effect, which describes the decrease in oxygen binding to hemoglobin in response to increased carbon dioxide and hydrogen ions, is not relevant at high oxygen concentrations.

**Clinical Pearl / High-Yield Fact**
Remember that the oxygen hemoglobin dissociation curve is sigmoid-shaped, meaning that small changes in partial pressure of oxygen can result in large changes in oxygen saturation at low partial pressures, but the curve levels off at high partial pressures.

**Correct Answer:** C. 98-99%