Final answer:
The total amount of exchangeable air is known as residual volume. Residual volume is the air left in the lungs if you exhale as much air as possible and is important for preventing the collapse of alveoli.
Step-by-step explanation:
The total amount of exchangeable air is known as residual volume. Residual volume (RV) is the air left in the lungs if you exhale as much air as possible. It makes breathing easier by preventing the alveoli from collapsing. Residual volume is important for preventing large fluctuations in respiratory gases and cannot be measured directly, but can only be calculated.