**Core Concept**
Acute intestinal obstruction in neonates is a medical emergency caused by a blockage in the small or large intestine. The most common cause of this condition is related to the incomplete rotation and fixation of the gut during fetal development, leading to a narrowing or obstruction of the intestinal lumen.

**Why the Correct Answer is Right**
The correct answer is Volvulus, which is a twisting of the intestine around its mesenteric axis. This twisting can cause a mechanical obstruction and compromise blood flow to the intestine, leading to ischemia and necrosis. The most common type of volvulus in neonates is the midgut volvulus, which occurs due to the incomplete rotation of the gut during fetal development. The mesenteric axis is the narrowest part of the intestine, and when the intestine twists around this point, it can cause a significant obstruction.

**Why Each Wrong Option is Incorrect**
* **Option A:** Duodenal atresia is a congenital anomaly that causes a complete obstruction of the duodenum, but it is not the most common cause of acute intestinal obstruction in neonates.
* **Option B:** Intussusception is a condition where one segment of the intestine invaginates into another, causing an obstruction. While it can occur in neonates, it is not the most common cause.
* **Option C:** Meconium ileus is a condition where the meconium is thick and sticky, causing an obstruction of the ileum. While it can occur in neonates, it is more common in premature infants.

**Clinical Pearl / High-Yield Fact**
Neonates with intestinal obstruction often present with bilious vomiting, abdominal distension, and a failure to pass meconium within the first 48 hours of life. A high index of suspicion is necessary to diagnose this condition early, as prompt surgical intervention is often required to prevent intestinal necrosis and other complications.

**Correct Answer:** C.