Which one of the following statements is not true?

Options

A. pH of drinkingg water should be between 5.5-9.5
B. Concentration of DO below 6 ppm is good from 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

Answer

To solve the question, we need to evaluate each of the four statements provided and identify which one is not true.

### Step-by-Step Solution:

1. **Evaluate Statement 1**:
- **Statement**: "pH of drinking water should be between 5.5 to 9.5."
- **Analysis**: Drinking water with a pH below 5.5 is considered acidic, and above 9.5 is considered basic. Both extremes can be harmful for consumption. Therefore, this statement is **true**.

2. **Evaluate Statement 2**:
- **Statement**: "Concentration of dissolved oxygen below 6 parts per million is good for growth of fish."
- **Analysis**: A concentration of dissolved oxygen below 6 parts per million is actually low and can hinder the growth of fish, as fish require sufficient oxygen for survival. Therefore, this statement is **false**.

3. **Evaluate Statement 3**:
- **Statement**: "Clean water would have a biological oxygen demand value of less than 5 ppm."
- **Analysis**: Biological Oxygen Demand (BOD) measures the amount of oxygen required by microorganisms to decompose organic matter in water. A BOD of less than 5 ppm indicates low organic matter and thus clean water. Therefore, this statement is **true**.

4. **Evaluate Statement 4**:
- **Statement**: "Oxides of sulphur, nitrogen, and carbon are the most widespread air pollutants."
- **Analysis**: These oxides are indeed common air pollutants resulting from industrial activities and vehicle emissions. Therefore, this statement is **true**.

### Conclusion:
After evaluating all statements, the one that is not true is **Statement 2**: "Concentration of dissolved oxygen below 6 parts per million is good for growth of fish."

### Final Answer:
The incorrect statement is **Statement 2**.

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