Which of the following describes the residual volume of the lungs?

Residual volume refers to the amount of air that remains in the lungs after a person has exhaled completely. This volume is crucial because it prevents the lungs from collapsing and ensures that there is always a certain amount of air present for gas exchange, even during exhalation. Understanding residual volume is important in various medical contexts, such as when assessing lung function or diagnosing certain respiratory conditions.

Other definitions associated with lung volumes help clarify why the correct choice fits the description accurately. For example, total lung capacity is the total volume of air the lungs can hold, while the tidal volume refers to the air that moves in and out during normal respiration. Knowing these definitions helps underscore the distinct role of residual volume in respiratory physiology.