Why does the rain water normally have a pH of about 5.6 ? When does it become acid rain ?

Explanation

### Step-by-Step Solution:

1. **Understanding the pH of Rainwater**:
- Rainwater typically has a pH of about 5.6, which indicates that it is slightly acidic. This acidity is primarily due to the presence of carbon dioxide (CO₂) in the atmosphere.

2. **Formation of Carbonic Acid**:
- When rainwater forms, it interacts with carbon dioxide in the atmosphere. The chemical reaction can be represented as:
\[
...