What term describes accumulation of air outside the lung but within the chest cavity?

• A. Pleural Effusion
• B. Embolism
• C. Pneumothorax
• D. Croup

Answer: (C)

Pneumothorax occurs when air collects in the pleural space—the gap between the lung surface and the chest wall. That space normally stays under negative pressure to keep the lung inflated; when air enters, the pressure balance is lost and the lung can collapse partially or fully. This description specifically refers to air in the chest outside the lung, which is exactly what a pneumothorax is. Pleural effusion would be fluid in that space, not air. Embolism involves a blood clot blocking a vessel, and croup is an airway infection causing swelling and a barking cough.