**Core Concept**
Esophageal atresia is a congenital anomaly characterized by the incomplete formation of the esophagus, often requiring radiographic diagnosis to determine its extent. The chosen contrast material must be safe for use in infants and provide adequate visualization of the esophageal lumen.

**Why the Correct Answer is Right**
Barium sulfate is commonly used as a contrast agent in esophageal atresia diagnosis due to its high density, which allows for clear visualization of the esophageal lumen on plain radiographs. However, it is not the preferred option in this scenario. The correct answer is a safer alternative.

**Why Each Wrong Option is Incorrect**
**Option A:** Gastrografin is a water-soluble contrast agent but is not typically used in esophageal atresia diagnosis due to its potential for causing severe chemical pneumonitis if aspirated.
**Option B:** Iodine-based contrast agents are also not suitable for this diagnosis as they can cause severe chemical pneumonitis if aspirated.
**Option C:** Air or gas is not a suitable contrast agent in diagnosing esophageal atresia as it does not provide clear visualization of the esophageal lumen.

**Clinical Pearl / High-Yield Fact**
When diagnosing esophageal atresia, it is crucial to use a contrast agent that is safe for use in infants and provides clear visualization of the esophageal lumen to avoid misdiagnosis.

**Correct Answer: C. Air or gas.**