Which one of the following statement is not true ?

Options

A. Oxides of sulphur, nitrogen and carbon are the most widespread air pollutant
B. pH of 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 determine which statement is not true, let's analyze each statement one by one:

### Step 1: Analyze the First Statement
**Statement:** Oxides of Sulphur, Nitrogen, and Carbon are the most widespread air pollutants.

- **Analysis:** This statement is true. The oxides of sulfur (like SO2, SO3), nitrogen (like NO, NO2), and carbon (like CO, CO2) are indeed among the most common air pollutants.

### Step 2: Analyze the Second Statement
**Statement:** The pH of drinking water should be in the range of 6.5 to 8.5.

- **Analysis:** This statement is also true. The acceptable pH range for drinking water is generally between 6.5 and 8.5, making it safe for consumption.

### Step 3: Analyze the Third Statement
**Statement:** The concentration of Dissolved Oxygen (DO) below 6 ppm is good for the growth of fish.

- **Analysis:** This statement is false. The concentration of dissolved oxygen below 6 ppm is not good for fish growth; in fact, it is detrimental. Fish require a minimum of around 6-8 ppm of dissolved oxygen to thrive. Therefore, this statement is incorrect.

### Step 4: Analyze the Fourth Statement
**Statement:** Clean water should have a Biological Oxygen Demand (BOD) value of less than 5 ppm.

- **Analysis:** This statement is true. Clean water typically has a BOD value of less than 5 ppm, indicating low levels of organic pollution and a healthy aquatic environment.

### Conclusion
After analyzing all statements, the statement that is not true is the third one regarding the concentration of dissolved oxygen.

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

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