Define vital capacity of lung.

Explanation

**Step-by-Step Solution:**

1. **Definition of Vital Capacity**: Vital capacity of the lung is defined as the maximum amount of air that can be expelled from the lungs after taking the deepest possible breath.

2. **Components of Vital Capacity**: It is calculated by adding three specific lung volumes:
- **Tidal Volume (TV)**: The amount of air inhaled or exhaled during normal breathing.
- **Inspiratory Reserve Volume (IRV)**: The additional air that can be inhaled after a normal inhalation.
- **Expiratory Reserve Volume (ERV)**: The additional air that can be forcibly exhaled after a normal exhalation.
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