**Core Concept**
Pyloric stenosis is a condition characterized by the narrowing of the pyloric channel, leading to gastric outlet obstruction. This condition often presents in infants and is associated with hypertrophy of the pyloric muscle.

**Why the Correct Answer is Right**
The correct answer is related to the pathophysiology of pyloric stenosis. In this condition, the pyloric muscle hypertrophies, leading to thickening of the pyloric wall. This thickening causes the pyloric channel to narrow, resulting in gastric outlet obstruction. The hypertrophied muscle is often associated with a characteristic "olive" mass palpable on abdominal examination.

**Why Each Wrong Option is Incorrect**
**Option A:** This option is not directly related to the pathophysiology of pyloric stenosis. While electrolyte imbalances can occur in conditions with gastric outlet obstruction, they are not a characteristic feature of pyloric stenosis.
**Option B:** This option is incorrect as it describes a characteristic feature of intestinal obstruction, not pyloric stenosis.
**Option C:** This option is not relevant to pyloric stenosis. Gastric mucosal hypertrophy is not a characteristic feature of this condition.

**Clinical Pearl / High-Yield Fact**
A key clinical feature of pyloric stenosis is the presence of projectile vomiting, which is often forceful and effortless. This symptom is due to the rapid emptying of the stomach contents into the small intestine.

**Correct Answer: A. Hypertrophy of the pyloric muscle.**