Question

what happens to the diaphragm and intercostal muscles during exhalation?
they relax
they spasm
they expand
they twitch
they contract

Explanation:

During exhalation, the diaphragm and intercostal muscles relax. When these muscles relax, the diaphragm moves upward (relaxes and domes up) and the intercostal muscles (external intercostal muscles relax while internal intercostal muscles may contract in forced exhalation, but in normal exhalation, the main relaxation is key). This relaxation reduces the volume of the thoracic cavity. According to Boyle's law (pressure and volume are inversely related at constant temperature for a given amount of gas), a decrease in volume leads to an increase in pressure within the lungs (intrapulmonary pressure becomes greater than atmospheric pressure). As a result, air is pushed out of the lungs (exhalation occurs). Spasming refers to involuntary muscle contractions which is not the normal process in exhalation. Expanding would increase volume (opposite of exhalation need). Twitching is an involuntary small - scale muscle movement not related to normal exhalation. Contracting (in the context of these muscles) is associated with inhalation (diaphragm contracts and flattens, external intercostal muscles contract to lift the rib cage, increasing thoracic volume).

Answer:

They relax.