**Core Concept**
Hyperrophic pyloric stenosis is a condition characterized by the thickening of the pyloric muscle, leading to gastric outlet obstruction. This obstruction results in the vomiting of food, which is rich in hydrochloric acid and pepsin. The loss of gastric contents leads to a metabolic disturbance, primarily due to the loss of hydrogen ions and chloride ions.

**Why the Correct Answer is Right**
The loss of hydrochloric acid (HCl) from the stomach leads to a metabolic alkalosis, as the body loses hydrogen ions (H+). This loss of H+ ions results in an increase in blood pH. The kidneys compensate for this increase in pH by excreting more bicarbonate ions (HCO3-) to maintain acid-base balance. This process is mediated by the renin-angiotensin-aldosterone system (RAAS), which increases sodium and water reabsorption in the collecting ducts, leading to volume contraction and hypochloremia.

**Why Each Wrong Option is Incorrect**
**Option A:** Metabolic acidosis is incorrect because the loss of hydrochloric acid leads to an increase in blood pH, resulting in alkalosis.
**Option B:** Hypokalemia may occur in some cases of pyloric stenosis due to vomiting, but it is not the primary metabolic disturbance.
**Option C:** Hypocalcemia is not directly related to the metabolic disturbance seen in pyloric stenosis.

**Clinical Pearl / High-Yield Fact**
In cases of pyloric stenosis, the metabolic alkalosis can be treated with the administration of hydrochloric acid or its equivalent, such as arginine hydrochloride, to replenish the lost hydrogen ions.

**Correct Answer: B. Hypochloremic metabolic alkalosis**