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

Explanation

To determine which statement is not true, we will analyze each statement one by one.

### Step 1: Analyze the first statement
**Statement 1**: "Oxide of Sulphur, Nitrogen, and Carbon are the most widespread air pollutants."

- This statement is true. Sulfur oxides (SOx), nitrogen oxides (NOx), and carbon oxides (CO and CO2) are indeed among the most common air pollutants found in the atmosphere.

### Step 2: Analyze the second statement
**Statement 2**: "pH of drinking water should be between 5.5 to 9.5."

- This statement is also true. The acceptable pH range for drinking water is generally between 6.5 and 8.5, but a range of 5.5 to 9.5 is often considered acceptable in various contexts.

### Step 3: Analyze the third statement
**Statement 3**: "Concentration of DO below 6 ppm is good for the growth of fish."

- This statement is not true. Dissolved oxygen (DO) levels below 6 ppm are generally considered low and can be harmful to fish. Most fish species require a minimum of 6-7 ppm of dissolved oxygen for healthy growth and survival.

### Step 4: Analyze the fourth statement
**Statement 4**: "Concentration of DO below 6 ppm is good for growth of fish."

- This statement is a repetition of the third statement and is also not true for the same reasons mentioned above.

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

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