The exzyme nitrogenase which is capable of nitrogen reduction present in

Answer

### Step-by-Step Solution:

1. **Understanding Nitrogenase**: The enzyme nitrogenase is crucial for the process of nitrogen fixation, which is the conversion of atmospheric nitrogen (N₂) into ammonia (NH₃). This process makes nitrogen available to plants in a usable form.

2. **Function of Nitrogenase**: Nitrogenase facilitates the reduction of atmospheric nitrogen. This means it helps in breaking the strong triple bond of nitrogen gas (N₂) and converting it into ammonia (NH₃), which can then be utilized by plants for growth.

3. **Location of Nitrogenase**: The nitrogenase enzyme is primarily found in certain microorganisms. These microorganisms are classified as prokaryotes, which include bacteria and cyanobacteria.

4. **Specific Microorganisms**: Among the prokaryotes, specific bacteria such as *Rhizobium* and certain cyanobacteria possess the nitrogenase enzyme. These bacteria often form symbiotic relationships with plants, particularly legumes, to aid in nitrogen fixation.

5. **Conclusion**: Therefore, the enzyme nitrogenase, which is capable of nitrogen reduction, is present in certain prokaryotic microorganisms, specifically in some bacteria and cyanobacteria.

### Final Answer:
The enzyme nitrogenase, which is capable of nitrogen reduction, is present in certain prokaryotic microorganisms, specifically in bacteria such as *Rhizobium* and in certain cyanobacteria.

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