Final answer:
A physical sign indicating a pneumothorax during a chest assessment is tracheal deviation toward the side opposite the pneumothorax.
Step-by-step explanation:
When assessing a patient's chest for signs of a pneumothorax, one physical sign that indicates the presence of a pneumothorax is deviation of the trachea toward the side opposite the pneumothorax. This occurs because the air that enters the pleural space causes the lung to collapse on the affected side, which can push the trachea away from that side due to the change in pressures within the thoracic cavity. Other signs that can be observed are decreased or absent breath sounds on the affected side, chest asymmetry, and impaired chest expansion on the side of the pneumothorax due to the lung collapse.