**Core Concept**
Conn's syndrome, also known as primary aldosteronism, is a condition characterized by the excessive production of aldosterone by the adrenal glands. This leads to hypertension, hypokalemia, and metabolic alkalosis. The underlying pathophysiological mechanism involves the renin-angiotensin-aldosterone system (RAAS), where aldosterone stimulates sodium retention and potassium excretion in the kidneys.

**Why the Correct Answer is Right**
The correct answer involves understanding the clinical features of Conn's syndrome. The key features include hypertension, hypokalemia (low potassium levels), and metabolic alkalosis (elevated blood pH). This is due to the aldosterone-induced sodium retention and potassium excretion in the kidneys.

**Why Each Wrong Option is Incorrect**
* **Option A:** is incorrect because it is a characteristic feature of Conn's syndrome. The excessive production of aldosterone leads to hypertension.
* **Option B:** is incorrect because it is a hallmark of Conn's syndrome. Hypokalemia is a common finding due to the potassium-wasting effect of aldosterone.
* **Option D:** is incorrect because it is a feature of Conn's syndrome. Metabolic alkalosis is a result of the increased sodium reabsorption and potassium excretion in the kidneys.

**Clinical Pearl / High-Yield Fact**
To remember the key features of Conn's syndrome, use the mnemonic "HYPK" - Hypertension, **Y**oung age, **P**otassium wasting, and **K**etosis (due to metabolic alkalosis).

**Correct Answer: A. Hypocalcemia.**