This question is on application of Boyle's law; <u>pressure is inversely proportional to volume</u>.when we inhale air, the diaphragm and the muscles in the ribs contract thus increasing the volume in the lungs.Increased volume of the lungs cause the pressure to decrease.During exhaling, the diaphragm and muscles in the ribs relax, making the lungs to recoil and reduce in volume to force air out.Pressure in the lungs is increased than that in the environment making air to move out.
