Lungs are made up of air-filled sacs, the alveoli. They do not collapse even after forceful expiration, because of :
Residual Volume
Inspiratory Reserve Volume
Tidal Volume
Expiratory Reserve Volume
As we have learnt in
Residual Volume (RV): Volume of air remaining in the lungs even after a forcible expiration. This averages 1100 mL to 1200 mL. It prevents lungs from collapsing.
Hence,t he correct answer is 'Residual Volume'
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