**Core Concept:**
The concept being tested in this question is the partial pressure of oxygen (PaO2) in the alveolar air, which is an important parameter in measuring the efficiency of gas exchange in the lungs. The partial pressure refers to the pressure exerted by the specific gas component in a mixture of gases, in this case, oxygen (O2) and carbon dioxide (CO2).

**Why the Correct Answer is Right:**
The correct answer (D) refers to the normal adult arterial oxygen saturation (SaO2), which is approximately 95-100%. Since the oxygen saturation is directly proportional to the oxygen partial pressure in the arterial blood, we can use the following formula to calculate the corresponding alveolar oxygen pressure (PaO2):

PaO2 = (SaO2 * 0.00316) + 47

**Why Each Wrong Option is Incorrect:**
A. This answer (A) is incorrect because it directly provides the value of PaO2, which is not the correct approach to solve the problem. PaO2 calculation requires SaO2, which is not given in the question.
B. This answer (B) is incorrect because it mentions the normal PaCO2, which is unrelated to the question about PaO2.
C. This answer (C) is incorrect as it provides a value for the alveolar-arterial oxygen gradient (AaDO2), which is different from the question's focus on PaO2.

**Why the Correct Answer is Right:**
The correct answer (D) provides the relationship between arterial oxygen saturation (SaO2) and alveolar oxygen pressure (PaO2), allowing us to estimate the PaO2 value based on the given SaO2 value.

**Clinical Pearl:**
In clinical practice, understanding the relationship between SaO2 and PaO2 is essential for diagnosing and managing respiratory and cardiovascular disorders. A significant decrease in SaO2 may indicate hypoxia, while a higher SaO2 than expected may indicate hyperoxia. Monitoring these parameters can help guide oxygen therapy, ventilation adjustments, and evaluate overall respiratory and cardiovascular health.