The air that remains in the lungs even after the most forceful expiration is the

Explanation

About 1,200 cm3 cannot be expelled, and this residual volume keeps the alveoli partly inflated so they do not collapse and stick shut, and it also lets gas exchange continue between breaths. Because it can never be breathed out, it cannot be measured with a simple spirometer. Its presence is also why lungs float in water, a fact used in forensic medicine to show that a baby breathed after birth.