**Core Concept**
Type-II respiratory failure, also known as hypercapnic respiratory failure, is a condition where there is an inability to adequately ventilate, leading to an accumulation of carbon dioxide (CO2) in the blood. This occurs when the respiratory system is unable to remove CO2 efficiently, often due to issues with lung function, neuromuscular disorders, or other factors.

**Why the Correct Answer is Right**
In type-II respiratory failure, the partial pressure of carbon dioxide (PaCO2) in arterial blood increases, while the partial pressure of oxygen (PaO2) may also decrease. This is due to the impaired lung function, which leads to a decrease in the alveolar ventilation rate. As a result, the body is unable to remove the excess CO2, leading to hypercapnia. The increased CO2 levels can have various effects on the body, including respiratory acidosis, increased respiratory rate, and altered consciousness.

**Why Each Wrong Option is Incorrect**
* **Option A:** This option is incorrect because it does not accurately describe the primary characteristic of type-II respiratory failure.
* **Option B:** This option is incorrect because it is more commonly associated with type-I respiratory failure, where there is a decrease in the partial pressure of oxygen (PaO2) without an increase in the partial pressure of carbon dioxide (PaCO2).
* **Option C:** This option is incorrect because it is not a direct consequence of type-II respiratory failure.

**Clinical Pearl / High-Yield Fact**
A key point to remember is that type-II respiratory failure is often associated with a history of chronic obstructive pulmonary disease (COPD), neuromuscular disorders, or other conditions that impair lung function.

**Correct Answer: D. Hypercapnia**