Final answer:
Tidal volume is the amount of air that leaves the lungs under normal conditions, which is typically around one-half liter.
Step-by-step explanation:
The amount of air that leaves the lungs under normal conditions is called the tidal volume (TV). Tidal volume is the volume of air inhaled or exhaled in a single, normal breath. On average, this volume is about one-half liter, which is akin to the capacity of a 20-ounce drink bottle. It is an essential component of lung volumes, which also includes the expiratory reserve volume, inspiratory reserve volume, and residual volume. Notably, the residual volume is the amount of air that remains in the lungs after a maximal, forceful exhalation, and it cannot be directly measured because the lungs cannot be completely emptied of air. This residual air helps in preventing the collapse of the lung tissues and maintains consistent concentrations of respiratory gases.