Biological oxygen demand of __ is the least.

Options

A. sewage
B. sea water
C. pure water
D. polluted water

Answer

To determine which option has the least Biological Oxygen Demand (BOD), we need to understand what BOD represents and how it varies among different types of water.

### Step-by-Step Solution:

1. **Understand Biological Oxygen Demand (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. **Identify the Types of Water**:
- The question presents three options: C-Water, Pure Water, and Polluted Water.

3. **Analyze Each Type of Water**:
- **Pure Water**: Contains very few organic materials and microorganisms. Therefore, it has a very low BOD.
- **Polluted Water**: Contains high levels of organic matter and microorganisms, leading to a high BOD due to increased oxygen consumption during decomposition.
- **C-Water**: The term is unclear without context, but if it refers to a type of water that is not pure or polluted, it would likely have a BOD that falls somewhere between pure and polluted water.

4. **Compare BOD Values**:
- Pure Water has the least BOD because it has minimal organic matter and microorganisms.
- Polluted Water has the highest BOD due to the presence of a lot of organic matter.
- C-Water's BOD would depend on its specific characteristics, but it is unlikely to be lower than that of Pure Water.

5. **Conclusion**:
- Based on the analysis, the Biological Oxygen Demand of Pure Water is the least.

### Final Answer:
The Biological Oxygen Demand of **Pure Water** is the least.

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