**Core Concept**
Congenital pyloric stenosis is a condition characterized by the narrowing of the pylorus, the passage that connects the stomach to the small intestine. This narrowing leads to gastric outflow obstruction, resulting in metabolic derangements due to chronic vomiting.

**Why the Correct Answer is Right**
The metabolic derangement in congenital pyloric stenosis is primarily due to the loss of hydrochloric acid (HCl) and bicarbonate ions (HCO3-) from the stomach through vomiting. The loss of HCl leads to a decrease in hydrogen ion concentration in the blood, causing metabolic alkalosis. Additionally, the loss of bicarbonate ions results in a decrease in the chloride ion concentration, leading to a contraction alkalosis. The kidneys compensate for the loss of hydrogen ions by retaining sodium and chloride ions, leading to an increase in sodium ion concentration and a decrease in potassium ion concentration, resulting in hypokalemia.

**Why Each Wrong Option is Incorrect**
* **Option A:** This option is incorrect because it does not accurately describe the metabolic derangement in congenital pyloric stenosis.
* **Option B:** This option is incorrect because it does not account for the loss of bicarbonate ions and the resulting contraction alkalosis.
* **Option D:** This option is incorrect because it does not accurately describe the metabolic derangement and does not account for the loss of potassium ions.

**Clinical Pearl / High-Yield Fact**
In cases of congenital pyloric stenosis, patients often present with projectile vomiting, which leads to dehydration and electrolyte imbalances. It is essential to monitor electrolyte levels, particularly potassium, and to correct any imbalances promptly to prevent complications.

**Correct Answer:** C. Metabolic alkalosis with contraction alkalosis and hypokalemia.