`BOD_(5)` is

Options

A. Waste decomposed in 5 days
B. Oxygen used in 5 days
C. Microorganisms killed in 5 days
D. Dissolved oxygen left after 5 days

Answer

To answer the question "BOD_(5) is", we need to understand what BOD stands for and what it signifies in the context of environmental chemistry.

### Step-by-Step Solution:

1. **Definition of BOD**:
BOD stands for Biological Oxygen Demand. It is a measure of the amount of oxygen that microorganisms will consume while decomposing organic matter in water.

2. **Understanding the '5' in BOD_(5)**:
The '5' in BOD_(5) refers to the duration of 5 days. This means that the measurement is taken over a period of 5 days.

3. **Temperature Consideration**:
The standard temperature for measuring BOD is typically 20 degrees Celsius. This ensures consistency in measurements.

4. **Purpose of BOD Measurement**:
BOD is used to assess the degree of pollution in water bodies. A higher BOD indicates a higher level of organic matter and, consequently, a greater demand for oxygen by microorganisms.

5. **Conclusion**:
Therefore, BOD_(5) specifically indicates the amount of oxygen consumed by microorganisms in a water sample over a period of 5 days at 20 degrees Celsius.

### Final Answer:
BOD_(5) is the amount of oxygen used by microorganisms in a water sample over a period of 5 days at a temperature of 20 degrees Celsius.

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