Final answer:
The correct treatment for a flail chest injury is positive pressure ventilation.
Step-by-step explanation:
The correct treatment for a flail chest injury is positive pressure ventilation. This involves the use of a mechanical ventilator to assist with breathing and maintain adequate oxygenation.
Other treatments mentioned in the options, such as positioning of comfort with O2 per NRB mask (option A), stabilization of the flail segment with a sandbag (option C), and applying tape to the uninjured side (option D), may provide some symptomatic relief but are not the primary treatment for a flail chest injury.