**Core Concept**
Congenital hypertrophic pyloric stenosis (CHPS) is a condition characterized by the thickening of the pyloric muscle, leading to gastric outlet obstruction in infants. This condition is often associated with a family history and is more common in males.

**Why the Correct Answer is Right**
The correct answer is related to the pathophysiology of CHPS. The thickening of the pyloric muscle is due to an increase in the smooth muscle mass and hypertrophy of the pyloric sphincter. This leads to a narrowing of the pyloric channel, causing gastric outflow obstruction. The obstruction prevents the stomach from emptying its contents into the small intestine, resulting in projectile vomiting.

**Why Each Wrong Option is Incorrect**
**Option A:** This option is incorrect because it is not a characteristic feature of CHPS. The thickening of the pyloric muscle is not due to an increase in the number of nerve cells.
**Option B:** This option is incorrect because the condition is not typically associated with a decrease in the number of smooth muscle cells. Instead, there is an increase in smooth muscle mass.
**Option C:** This option is incorrect because it is not a primary cause of CHPS. While some cases may have a familial component, it is not the primary reason for the thickening of the pyloric muscle.

**Clinical Pearl / High-Yield Fact**
A classic clinical feature of CHPS is the "olive" mass palpable in the right upper quadrant, which is the hypertrophied pylorus. This finding is often associated with a palpable, smooth, and firm mass.

**Correct Answer: D.**