**Core Concept**
The given arterial blood gas (ABG) values are used to assess the acid-base balance in the patient. The **pH** indicates the level of acidity or alkalinity, **HCO3 (bicarbonate)** is a measure of the metabolic component, and **pCO2 (partial pressure of carbon dioxide)** reflects the respiratory component.

**Why the Correct Answer is Right**
Given the **pH** of 7.2, which is lower than the normal range (7.35-7.45), indicating **acidosis**. The **HCO3** level is elevated at 38 mmol/L (normal range: 22-28 mmol/L), suggesting a **metabolic alkalosis** component. However, the high **pCO2** of 56 mm Hg (normal range: 35-45 mm Hg) points towards a **respiratory acidosis**. The combination of an elevated **HCO3** and high **pCO2** with a low **pH** suggests a mixed disorder, but the primary issue here is the respiratory component causing acidosis, with the kidneys attempting to compensate for the chronic respiratory issue by retaining more bicarbonate.

**Why Each Wrong Option is Incorrect**
**Option A:** Would be incorrect if it suggested a pure metabolic cause without considering the respiratory component.
**Option B:** Might be considered if it represented a condition without the metabolic compensation seen with the elevated **HCO3**.
**Option C:** Could be a possibility if the question hinted at a different primary disturbance, but given the data, it doesn't fit as well as the correct interpretation.
**Option D:** Would not align with the provided ABG values if it suggested a condition not consistent with the observed **pH**, **HCO3**, and **pCO2** levels.

**Clinical Pearl / High-Yield Fact**
In interpreting ABG results, it's crucial to consider all three components (**pH**, **HCO3**, and **pCO2**) to accurately determine the acid-base disorder. An elevated **HCO3** with acidosis (low **pH**) can indicate a chronic respiratory acidosis with renal compensation.

**Correct Answer:** D. Mixed respiratory and metabolic acidosis