Which one of the following statements 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 from the options provided, we will analyze each statement step by step.

### 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), nitrogen (like NOx), and carbon (like CO and 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 typically between 6.5 and 8.5, which is considered 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. A dissolved oxygen level below 6 ppm is not good for fish; in fact, it is considered low and can be harmful to aquatic life. Fish generally require a DO level above 6 ppm for healthy growth and survival.

### Step 4: Analyze the fourth statement
**Statement:** Clean water should have a BOD value less than 5 ppm.

- **Analysis:** This statement is true. A Biological Oxygen Demand (BOD) value of less than 5 ppm indicates that the water is relatively clean and has a low level of organic pollution.

### Conclusion
After analyzing all the statements, the statement that is not true is the third one regarding the concentration of Dissolved Oxygen (DO) being below 6 ppm being good for fish growth.

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

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