What is the amount of air that enters the lungs during each breath?

Tidal volume is the correct choice as it refers to the amount of air that is inhaled or exhaled during a normal breath when at rest. This measurement typically averages around 500 milliliters for a healthy adult under resting conditions. It represents the regular airflow during quiet breathing cycles, which is crucial for maintaining the exchange of oxygen and carbon dioxide in the lungs.

Other volumes like inspiratory reserve volume pertain to additional air that can be inhaled after a normal inhalation, and vital capacity includes the maximum amount of air that can be forcibly exhaled after a deep inhalation. Residual volume, on the other hand, is the air that remains in the lungs after a forceful exhalation, ensuring the alveoli stay inflated and facilitating gas exchange between breaths. Thus, tidal volume specifically answers the question regarding the air entering the lungs with every standard breath.