Which one of the following statement is not true?

Options

A. pH of drinking water should be between 5.5-9.5
B. Concentration of DO below 6 ppm is good for the growth of fish.
C. Clean water would have a BOD value of less than 5 ppm.
D. Oxides of sulphur, nitrogen and carbon, are the most widespread air pollutant.

Explanation

To determine which statement is not true regarding environmental pollution, we will analyze each statement provided in the question.

### Step 1: Analyze each statement

1. **pH of drinking water should be between 5.5 to 9.5.**
- This statement is true. The acceptable pH range for drinking water is indeed between 5.5 and 9.5, as it ensures safety and palatability.

2. **Concentration of DO below 6 ppm is good for the growth of fish.**
- This statement is false. A dissolved oxygen (DO) concentration below 6 ppm is not good for fish; in fact, it is harmful and can lead to fish mortality. Fish require adequate levels of dissolved oxygen to survive.

3. **Clean water would have a BOD value of less than 5 ppm.**
- This statement is true. Clean water typically has a Biochemical Oxygen Demand (BOD) of less than 5 ppm, indicating low levels of organic pollution.

4. **Oxides of Sulphur, Nitrogen, and Carbon are the most widespread air pollutants.**
- This statement is true. These oxides are indeed among the most common air pollutants and contribute to various environmental issues, including acid rain and smog.

### Conclusion
After analyzing all the statements, we find that the second statement, "Concentration of DO below 6 ppm is good for the growth of fish," is not true.

### Final Answer
The statement that is not true is: **"Concentration of DO below 6 ppm is good for the growth of fish."**

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