Final answer:
A pneumothorax is a collapsed lung that occurs due to the presence of air in the intrapleural space. It can be caused by trauma or weak connective tissue, and symptoms include chest pain and shortness of breath.
Step-by-step explanation:
A pneumothorax is a collapsed lung that occurs due to the presence of air in the intrapleural space, the space between the visceral and parietal pleurae. This can happen as a result of trauma, such as a broken rib puncturing the lung, or spontaneously in individuals with weak connective tissue. Symptoms may include chest pain, shortness of breath, and decreased breath sounds on the affected side.