At which of the following pH, rain is called as acid rain?

Options

A. 4
B. 6
C. 6.8
D. All of these

Answer

To determine at which pH rain is classified as acid rain, we can follow these steps:

### Step-by-Step Solution:

1. **Understanding Acid Rain**:
- Acid rain is defined as rain that has a low pH, indicating it is acidic.

2. **Normal pH of Rain**:
- The pH of normal rainwater is typically between 5 and 6. This means that rainwater is slightly acidic under normal conditions.

3. **Definition of Acid Rain**:
- Rain is classified as acid rain when its pH falls below the normal range of 5 to 6. Therefore, if the pH is less than 5, it is considered acid rain.

4. **Analyzing the Options**:
- We need to evaluate the given options to find out which one indicates a pH that is less than 5.
- Option 1: pH 4 (this is less than 5, so it is acid rain).
- Option 2: pH 6 (this is within the normal range, so it is not acid rain).
- Option 3: pH 6.8 (this is also above the normal range, so it is not acid rain).
- Option 4: "All of these" (this cannot be correct since not all options are acid rain).

5. **Conclusion**:
- Based on the analysis, the only option that indicates acid rain is Option 1, which is pH 4.

### Final Answer:
- The pH at which rain is called acid rain is **pH 4**.

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