What are the factors on which vital capacity of lungs depend ?

Explanation

**Step-by-Step Solution:**

1. **Definition of Vital Capacity**: Vital capacity refers to the maximum amount of air a person can expel from their lungs after taking a maximum inhalation. It is an important measure in respiratory physiology.

2. **Normal Range**: For an average adult, the vital capacity typically ranges from 4,000 to 4,500 ml.

3. **Factors Affecting Vital Capacity**:
- **Age**: As a person ages, the capacity of the lungs tends to decrease. This is due to the loss of elasticity and strength in the lung tissues and respiratory muscles.
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