**Core Concept**
The infant's symptoms and chest X-ray findings are suggestive of a respiratory illness characterized by airway obstruction, hyperinflation, and increased work of breathing. This condition is often a complication of a viral upper respiratory infection in young children.

**Why the Correct Answer is Right**
The infant's presentation is consistent with bronchiolitis, a common lower respiratory tract infection in infants less than 2 years of age. The condition is characterized by inflammation and obstruction of the small airways (bronchioles) due to the production of excess mucus and the swelling of the airway walls. This leads to increased resistance to airflow, resulting in the infant's symptoms of cough, wheezing, and difficulty breathing. The chest X-ray findings of hyperinflation are also consistent with bronchiolitis, as the infant's lungs are over-inflated due to the air trapping caused by the obstruction of the small airways.

**Why Each Wrong Option is Incorrect**
* **Option A:** This option is incorrect because bronchiolitis is not typically associated with a productive cough, as the infant's airways are more likely to be obstructed by excess mucus than producing it.
* **Option B:** This option is incorrect because asthma is a chronic condition that typically presents with episodic symptoms of wheezing, coughing, and shortness of breath, and is not typically associated with a viral upper respiratory infection.
* **Option C:** This option is incorrect because pneumonia is a more severe infection of the lung parenchyma, typically associated with a more severe presentation, including fever, lethargy, and chest X-ray findings of consolidation, rather than hyperinflation.
* **Option D:** This option is incorrect because cystic fibrosis is a genetic disorder that affects the production of mucus in the lungs, leading to recurrent respiratory infections and lung damage, but is not typically associated with a viral upper respiratory infection.

**Clinical Pearl / High-Yield Fact**
Bronchiolitis is a common condition in infants and young children, and its diagnosis is often based on clinical presentation and chest X-ray findings, rather than laboratory tests. It is essential to recognize the signs and symptoms of bronchiolitis to provide prompt and effective management, including oxygen therapy, hydration, and supportive care.

**Correct Answer: B. Asthma**