**Core Concept:**
Pheochromocytoma is a rare tumor that originates from chromaffin cells in the adrenal medulla or sympathetic nerve plexus. It causes excessive secretion of catecholamines, leading to a range of clinical features.

**Why the Correct Answer is Right:**
The correct answer, **D**, is "hypokalemia" because pheochromocytomas primarily affect catecholamine levels, not potassium balance. While hypokalemia can occur due to various causes, it is not specifically associated with pheochromocytoma.

**Why Each Wrong Option is Incorrect:**

A. **Hypotension:** Although pheochromocytomas can cause hypertension, hypotension is not a typical feature due to the complex regulation of blood pressure by the autonomic nervous system.

B. **Hypoglycemia:** Pheochromocytomas primarily affect catecholamine levels and blood pressure, not glucose homeostasis. Hypoglycemia is not a typical feature.

C. **Hypokalemia:** As explained above, hypokalemia is not specifically associated with pheochromocytoma; it can result from various causes unrelated to catecholamine excess.

**Clinical Pearl / High-Yield Fact:**
A high index of suspicion for pheochromocytoma is essential because it can be a life-threatening condition, mimicking other diseases like severe hypertension or stroke. Early diagnosis and treatment are crucial to prevent complications such as stroke, myocardial infarction, or even death due to severe hypertension.

**Correct Answer:** D. Hypokalemia