The volume of air remaining in the respiratory passages and lungs after forceful expiration is called:

The volume of air remaining in the respiratory passages and lungs after forceful expiration is called "residual volume." This residual volume is an important aspect of lung function, as it ensures that there is always a certain amount of air in the lungs, preventing complete collapse of the alveoli and allowing for efficient gas exchange during the next inhalation. It is typically measured in milliliters and varies between individuals based on factors like age, sex, body size, and physical fitness. Understanding residual volume is crucial in fields such as medicine and exercise physiology, as it helps assess lung capacity and respiratory health.