If air enters the intrapleural space (the space between the pleura), a. a lobe of the lung can collapse. b. the lungs could swell and burst. c. the diaphragm will contract. d. nothing will happen because air is needed in the intrapleural space.

The intrapleural space, also known as the pleural cavity, is a thin fluid-filled space between the lungs and the chest wall. This space contains the pleural fluid, which helps in reducing friction between the chest wall and the lungs as the person breathes in and out.

If air enters the intrapleural space, it causes a condition called pneumothorax. Pneumothorax disrupts the equilibrium within the intrapleural space, and the lung may collapse as the pressure created by the air entering the intrapleural space causes the lung tissue to be pushed away from the chest wall.

a. A lobe of the lung can collapse: As mentioned earlier, the presence of air in the intrapleural space causes pressure imbalance leading to a collapsed lung, making this option correct. b. The lungs could swell and burst: Though pneumothorax can cause severe lung damage, it's not a direct cause for lung swelling and bursting. Thus, this option is incorrect. c. The diaphragm will contract: The diaphragm contracts during inhalation, allowing the lungs to expand. However, the air entering the intrapleural space doesn't necessarily cause the diaphragm to contract. This option is incorrect. d. Nothing will happen because air is needed in the intrapleural space: Air is not needed in the intrapleural space, and its presence can cause undesirable consequences like lung collapse. This option is incorrect. Hence, the correct answer to the given question is: a. If air enters the intrapleural space, a lobe of the lung can collapse.