AIIMS 2018 Zoology Lung Volumes and Capacities MCQ Question

Residual air, or the air that remains in the lungs after a forceful expiration, primarily resides in the alveoli, which are the tiny air sacs where gas exchange occurs. This residual volume is crucial for maintaining a constant exchange of O₂ and CO₂, ensuring that the blood remains oxygenated even between breaths. In contrast, the nostrils, bronchus, and trachea are part of the conducting zone of the respiratory system, which does not participate in gas exchange and does not retain residual air.