Ans. (b) Lung Laceration* The image shows presence of subcutaneous emphysema which is also hinted in line 2 of the question where it mentions crepitus is palpated.* Chest trauma, a major cause of subcutaneous emphysema, can cause air to enter the skin of the chest wall from the neck or lung.* Most students mark it as renal shut down which is not the answer because it would not happen within 4 hour of trauma insult.* Gas gangrene will again take time to develop and would lead to development of crepitus in the injured part.Causes of subcutaneous emphysema* Trauma to parts of the respiratory system other than the lungs, such as rupture of a bronchial tube, may also cause subcutaneous emphysema* May also occur with fractures of the facial bones, neoplasms, during asthma attacks.When the alveoli of the lung are ruptured, as occurs in pulmonary laceration, air may travel beneath the visceral pleura (the membrane lining the lung), to the hilum of the lung, up to the trachea, to the neck and then to the chest wall