With regard to the biological nitrogen fixation by Rhizobium in association with soya bean, which one of the following statement/statements does not hold true?

Options

A. Nitrogenase may require oxygen for its functioning
B. nitrogenase is Mo-Fe protein
C. Leghaemoglobin is a pink coloured pigment
D. Nitrogenase helps to convert `N_(2)` gas into two molecules of ammonia.

Explanation

### Step-by-Step Solution:

1. **Understanding Biological Nitrogen Fixation**:
- Biological nitrogen fixation is the process by which nitrogen gas (N₂) from the atmosphere is converted into ammonia (NH₃) by certain bacteria, such as Rhizobium, which form symbiotic relationships with leguminous plants like soybeans.

2. **Role of Rhizobium**:
- Rhizobium bacteria infect the root hairs of leguminous plants. This infection leads to the formation of root nodules where nitrogen fixation occurs.

3. **Function of Nitrogenase**:
- The enzyme nitrogenase is crucial for the nitrogen fixation process. It catalyzes the conversion of nitrogen gas into ammonia.

4. **Presence of Leghemoglobin**:
- In the root nodules, leghemoglobin is produced. This pink-colored pigment serves to bind oxygen, maintaining a low oxygen environment necessary for nitrogenase to function effectively.

5. **Oxygen Requirement**:
- A key point is that nitrogenase requires an anaerobic (absence of oxygen) environment to function. The statement "nitrogenase may require oxygen for its functioning" is incorrect because the presence of oxygen inhibits nitrogenase activity.

6. **Identifying the Incorrect Statement**:
- Among the statements provided, the one that does not hold true is: "Nitrogenase may require oxygen for its functioning." This is false as nitrogenase operates best in the absence of oxygen.

### Final Answer:
- The statement that does not hold true is: **"Nitrogenase may require oxygen for its functioning."**

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