Which one of the following statement is not true

Options

A. Clean water would have a BOD value of 5 ppm.
B. Fluoride deficiency in drinking water is harmful. Soluble fluoride is often used to bring its concentration upto 1 ppm
C. When pH of rain water is higher than 6.5, it is called acid rain
D. Dissolved Oxygen (DO) in cold water can reach a concentration upto 10 ppm

Answer

To determine which statement is not true regarding the BOD (Biochemical Oxygen Demand) of clear water, we need to analyze the provided statements.

### Step-by-Step Solution:

1. **Understanding BOD**:
- BOD is a measure of the amount of oxygen that microorganisms will consume while decomposing organic matter in water. It is an important indicator of water quality.

2. **Analyzing the Statement**:
- The statement in question is that "clear water would have a BOD volume of 5 ppm."
- Typically, clear water, which is often considered to be free from significant organic pollution, would have a low BOD value.

3. **Typical BOD Values**:
- Generally, BOD values for clean, unpolluted water are usually below 5 ppm. Values around 1-2 ppm are common for very clean water, while 5 ppm is often considered to be on the higher side for clear water.

4. **Conclusion**:
- Since the statement claims that clear water has a BOD volume of 5 ppm, and considering that clear water typically has a lower BOD value, we can conclude that this statement is not true.

### Final Answer:
The statement "clear water would have a BOD volume of 5 ppm" is not true.

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