**Core Concept**
Congenital hypertrophic pyloric stenosis (CHPS) is a condition characterized by thickening of the pyloric muscle, leading to gastric outlet obstruction in infants. This results in projectile vomiting, dehydration, and electrolyte imbalance. The pathophysiology involves an imbalance between the growth of the pyloric muscle and the pyloric channel, leading to obstruction.

**Why the Correct Answer is Right**
The correct answer is related to the pathophysiology of CHPS. The thickened pyloric muscle is composed of hypertrophied smooth muscle cells, which are rich in contractile elements. This hypertrophy is thought to be due to an imbalance between the growth of the pyloric muscle and the pyloric channel, leading to obstruction. The increased muscle thickness and contractility result in a narrowed pyloric channel, preventing the normal passage of gastric contents into the duodenum.

**Why Each Wrong Option is Incorrect**
**Option A:** This option is incorrect because it does not accurately describe the pathophysiology of CHPS. While electrolyte imbalance is a common complication of CHPS, it is not a direct result of the thickening of the pyloric muscle.
**Option B:** This option is incorrect because it is a symptom of CHPS, not a characteristic of the condition itself. Projectile vomiting is a clinical feature of CHPS, but it does not explain the underlying pathophysiology.
**Option C:** This option is incorrect because it is a characteristic of another condition, not CHPS. Duodenal atresia is a congenital condition characterized by a complete obstruction of the duodenum, whereas CHPS is a condition of the pylorus.

**Clinical Pearl / High-Yield Fact**
A key clinical feature of CHPS is the "olive" sign, which is a palpable mass in the right upper quadrant of the abdomen. This mass is the hypertrophied pyloric muscle and is a characteristic finding in infants with CHPS.

**Correct Answer:** .