**Core Concept**
Type II respiratory failure, also known as hypercapnic respiratory failure, is a condition characterized by impaired gas exchange in the lungs, leading to both hypoxemia (low PaO2) and hypercapnia (elevated PaCO2). This occurs when the respiratory system is unable to effectively remove carbon dioxide from the blood, resulting in a buildup of CO2 and a decrease in oxygen levels.

**Why the Correct Answer is Right**
The correct answer, **C. Low PaO2 / High PaCO2**, reflects the hallmark features of Type II respiratory failure. The impaired gas exchange in the lungs results in a decrease in oxygen levels (low PaO2), while the inability to effectively remove CO2 leads to an increase in PaCO2. This is often seen in conditions such as chronic obstructive pulmonary disease (COPD), pneumonia, or acute respiratory distress syndrome (ARDS), where the lungs are unable to meet the body's oxygenation and ventilation needs.

**Why Each Wrong Option is Incorrect**
**Option A:** Low PaO2 / Low PaCO2 is incorrect because it describes a state of hypoxemia without hypercapnia, which is more characteristic of Type I respiratory failure.

**Option B:** Normal PaCO2 / Low PaO2 is incorrect because it suggests that the patient is normocapnic (normal PaCO2 levels), which is not consistent with the definition of Type II respiratory failure.

**Option D:** High PaO2 / Low PaCO2 is incorrect because it describes a state of hypocapnia (low PaCO2 levels) without hypoxemia, which is not consistent with Type II respiratory failure.

**Clinical Pearl / High-Yield Fact**
In patients with Type II respiratory failure, the administration of oxygen can sometimes worsen the condition, as it can lead to further depression of respiratory drive and increased CO2 levels. Therefore, it is essential to carefully manage oxygen therapy in these patients to avoid exacerbating the condition.

**✓ Correct Answer: C. Low PaO2 / High PaCO2**