What is meant by : Residual air

Explanation

**Step-by-Step Solution:**

1. **Definition of Residual Air**: Residual air, also known as residual volume, refers to the volume of air that remains in the lungs after a person has exhaled forcefully or maximally.

2. **Importance of Residual Air**:
- **Prevention of Lung Collapse**: The presence of residual air is crucial because it prevents the lungs from collapsing. If the lungs were to collapse, it could lead to severe respiratory issues or even death.
- **Gas Exchange**: Residual air allows for continuous gas exchange in the lungs, even when a person is not actively inhaling or exhaling. This ensures that oxygen can still be absorbed and carbon dioxide can be expelled.

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