After the gaseous exchange in lungs, the impure air is expelled out in exhalation. The ribs muscles relax, bringing the ribs back to the orignal position. The diaphragm muscles also relax and it gets rise it dome shape. Increase of lung pressure:- Relaxation of diaphragm muscles reduce the space in chest cavity and increase pressure on lungs. The lungs contract and airexpelled out of them. Correct Answer After the gaseous exchange in lungs, the impure air is expelled out in exhalation. The ribs muscles relax, bringing the ribs back to the orignal position. The diaphragm muscles also relax and it gets rise it dome shape. Increase of lung pressure:- Relaxation of diaphragm muscles reduce the space in chest cavity and increase pressure on lungs. The lungs contract and air expelled out of them.