**Core Concept**
Pyloric stenosis is a condition characterized by the narrowing of the pyloric channel, which is the passage between the stomach and small intestine. This narrowing leads to gastric outlet obstruction, resulting in vomiting and specific electrolyte imbalances.

**Why the Correct Answer is Right**
The correct answer is C. 1 true 2,3,4,5 false. The feature of pyloric stenosis that is true is hypokalemic alkalosis (Option 1). This occurs due to prolonged vomiting, which leads to the loss of hydrogen ions and potassium ions. The loss of hydrogen ions results in metabolic alkalosis, while the loss of potassium ions leads to hypokalemia. The other options are false because peristalsis in pyloric stenosis is from left to right, not right to left (Option 2). Pyloric stenosis is commonly caused by hypertrophic pyloric stenosis, not carcinoma of the stomach (Option 3). Retention vomiting is not typically present in pyloric stenosis, as the obstruction is at the pyloric channel (Option 4). Finally, pyloric stenosis is more commonly seen in males than females (Option 5).

**Why Each Wrong Option is Incorrect**
**Option A:** This option suggests that Options 1, 2, 3 are true, and Options 4, 5 are false. However, Options 2, 3, and 5 are false, making this option incorrect.

**Option B:** This option suggests that Options 1, 2, 5 are true, and Options 3, 4 are false. However, Options 2, 5 are false, making this option incorrect.

**Option D:** This option suggests that all statements are true. However, Options 2, 3, 4, and 5 are false, making this option incorrect.

**Clinical Pearl / High-Yield Fact**
One key feature of pyloric stenosis is the presence of a palpable olive-shaped mass in the right upper quadrant, which is the hypertrophied pylorus. This mass is often tender to palpation and can be felt in the majority of cases.

**✓ Correct Answer: C. 1 true 2,3,4,5 false**