Which one of the following statements is not true ?

Options

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

Answer

To solve the question, "Which one of the following statements is not true?", we will analyze each option provided in the question.

### Step-by-Step Solution:

1. **Analyze Option 1**:
- The statement claims that the pH of drinking water should be between 5.5 to 9.5.
- **Understanding pH**:
- A pH of less than 7 indicates acidity, a pH of 7 is neutral, and a pH greater than 7 indicates basicity.
- The acceptable pH range for drinking water is indeed between 5.5 and 9.5.
- **Conclusion**: This statement is **true**.

2. **Analyze Option 2**:
- The statement claims that the concentration of Dissolved Oxygen (DO) below 6 ppm is good for the growth of fish.
- **Understanding Dissolved Oxygen**:
- The ideal concentration of DO for fish growth is around 8 mg/L (which is equivalent to 8 ppm).
- A DO level below 7 mg/L can lead to diseases in fish, and levels below 2 mg/L can be lethal.
- **Conclusion**: This statement is **false** (not true).

3. **Analyze Option 3**:
- The statement claims that clean water would have a BOD (Biochemical Oxygen Demand) value of less than 5 ppm.
- **Understanding BOD**:
- A lower BOD value indicates less pollution. Clean water typically has a BOD of less than 5 ppm.
- **Conclusion**: This statement is **true**.

4. **Analyze Option 4**:
- The statement claims that oxides of Sulphur, Nitrogen, and Carbon are the most widespread air pollutants.
- **Understanding Air Pollutants**:
- These oxides are indeed major contributors to air pollution, primarily from vehicles and industrial activities.
- **Conclusion**: This statement is **true**.

### Final Conclusion:
- The only statement that is not true is **Option 2**, which incorrectly states that a DO concentration below 6 ppm is good for the growth of fish.

### Summary of the Answer:
The statement that is **not true** is **Option 2**: "The concentration of DO below 6 ppm is good for the growth of fish."

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