Which of the following elements is required for the activity of nitrate reductase?

Options

A. Molybdenum
B. Zinc
C. Iron
D. Copper

Answer

### Step-by-Step Solution:

1. **Understanding the Question**: The question asks which element is required for the activity of nitrate reductase, an enzyme involved in nitrogen assimilation.

2. **Identifying the Function of Nitrate Reductase**: Nitrate reductase is an enzyme that reduces nitrate (NO3-) to nitrite (NO2-). This is an important step in the nitrogen assimilation process in plants.

3. **Recognizing the Role of Elements**: Various minerals play roles in enzyme activities. In the case of nitrate reductase, specific elements are known to be essential for its function.

4. **Evaluating the Options**: The options provided are molybdenum, zinc, iron, and copper. We need to determine which of these is specifically required for nitrate reductase activity.

5. **Identifying the Correct Element**: Molybdenum is known to be a crucial cofactor for nitrate reductase. It is involved in the enzyme's active site and is necessary for its catalytic activity.

6. **Conclusion**: Based on the information, the element required for the activity of nitrate reductase is molybdenum.

### Final Answer:
The element required for the activity of nitrate reductase is **molybdenum**.

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