**Core Concept**
Hypertrophic pyloric stenosis is a condition characterized by the thickening of the pyloric muscle, leading to gastric outlet obstruction. This condition often presents in infants, causing projectile vomiting, dehydration, and electrolyte imbalances.

**Why the Correct Answer is Right**
The metabolic disturbance in hypertrophic pyloric stenosis is primarily due to the loss of gastric contents, including hydrochloric acid (HCl) and potassium ions (K+). The frequent vomiting leads to hypochloremic, hypokalemic metabolic alkalosis. The loss of HCl results in a decrease in chloride ions, causing the kidneys to reabsorb more bicarbonate ions, leading to an increase in blood pH. Concurrently, the loss of K+ ions depletes the body's stores, leading to hypokalemia.

**Why Each Wrong Option is Incorrect**
**Option A:** This option is incorrect because it doesn't accurately describe the primary metabolic disturbance in hypertrophic pyloric stenosis. While dehydration is a common complication, it is not the primary metabolic disturbance.
**Option B:** This option is incorrect because it doesn't account for the specific electrolyte imbalances caused by the loss of gastric contents.

**Clinical Pearl / High-Yield Fact**
In cases of hypertrophic pyloric stenosis, the metabolic alkalosis is often associated with a high anion gap, which can be a clue to the correct diagnosis.

**Correct Answer: D. Hypochloremic, hypokalemic metabolic alkalosis.**