Question

during expiration...
multiple choice
increased alveolar volume causes decreased alveolar pressure
increased alveolar volume causes increased alveolar pressure
decreased alveolar volume causes increased alveolar pressure
decreased alveolar volume causes decreased alveolar pressure

Explanation:

During expiration, the diaphragm and intercostal muscles relax. This leads to a decrease in the volume of the thoracic cavity. According to Boyle's law ($P_1V_1 = P_2V_2$, where pressure $P$ and volume $V$ are inversely related when temperature is constant), a decrease in alveolar volume (due to the reduced thoracic cavity volume) causes an increase in alveolar pressure (air moves out of the lungs from an area of higher pressure in the alveoli to the lower - pressure environment outside the body).

Answer:

Decreased alveolar volume causes increased alveolar pressure.