**Core Concept**
Laryngomalacia is a congenital condition characterized by the softening of the laryngeal cartilages, particularly the supraglottic area, leading to partial airway obstruction during inspiration. This condition is often asymptomatic but can cause significant respiratory distress in infants.

**Why the Correct Answer is Right**
The diagnosis of laryngomalacia is primarily based on clinical evaluation and visualization of the laryngeal structures during inspiration. A flexible laryngoscopy is the best diagnostic tool to assess the degree of airway obstruction and the mobility of the supraglottic structures. This procedure allows the examiner to visualize the laryngeal opening and assess the severity of the laryngomalacia.

**Why Each Wrong Option is Incorrect**
**Option A:** Chest X-ray is not a reliable method for diagnosing laryngomalacia as it does not directly visualize the laryngeal structures.
**Option B:** Blood gas analysis may show signs of respiratory distress but is not specific for diagnosing laryngomalacia.
**Option C:** CT or MRI scans may provide additional information but are not the best initial diagnostic tools due to radiation exposure and cost.

**Clinical Pearl / High-Yield Fact**
Laryngomalacia often presents with symptoms such as stridor, apnea, and feeding difficulties in infants, and a high index of suspicion is necessary for early diagnosis and management.

**Correct Answer:** C. Flexible laryngoscopy.