The air that remains in the lungs after a maximal expiration

• A. Tidal Volume
• B. Functional Residual Capacity
• C. Residual Volume
• D. Vital Capacity

Answer: (C)

The air that remains in the lungs after a maximal expiration is residual volume. This is the portion of air that cannot be expelled, keeping the lungs from collapsing and ensuring a constant exchange of gases between breaths. It isn’t measured by a standard spirometry test because it cannot be exhaled; special techniques like body plethysmography or gas dilution are used to estimate it. For context, tidal volume is the amount moved in a normal breath, functional residual capacity is the air left after a normal exhale (including residual volume plus the expiratory reserve), and vital capacity is the total amount you can exhale after a maximal inhalation (the sum of the inspiratory reserve, tidal volume, and expiratory reserve).