When does a rain is considered to be acid rain ?

Explanation

### Step-by-Step Solution:

1. **Definition of Acid Rain**:
Acid rain is defined as any form of precipitation (rain, snow, sleet, or hail) that has a pH level lower than 5.6. This indicates that the rainwater is more acidic than normal.

2. **Chemical Reactions Involved**:
Acid rain is primarily caused by the presence of certain pollutants in the atmosphere. The main compounds responsible for acid rain are sulfur oxides (SOx) and nitrogen oxides (NOx).

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