Nitrogen fixation can be done by

Options

A. industries
B. Rhizobium
C. lightning
D. all of these.

Explanation

**Step-by-Step Solution:**

1. **Understanding Nitrogen Fixation:**
- Nitrogen fixation is the process of converting atmospheric nitrogen (N₂) into ammonia (NH₃), which can be used by plants. Atmospheric nitrogen is not directly usable by plants, so it needs to be converted into a form they can absorb.

2. **Identifying the Sources of Nitrogen Fixation:**
- Nitrogen fixation can occur through various means:
- **Biological Nitrogen Fixation:** This is primarily done by certain bacteria, such as *Rhizobium*, which live in symbiosis with leguminous plants. These bacteria convert atmospheric nitrogen into ammonia.
- **Physical Processes:** Lightning and ultraviolet (UV) radiation can provide the energy needed to convert nitrogen gas into nitrogen oxides, which can then be further processed into usable forms of nitrogen.
- **Industrial Processes:** Industries can also fix nitrogen through various chemical processes, including combustion in power plants and other industrial activities.

3. **Evaluating the Options:**
- The question provides the following options:
- Industries
- Rhizobium
- Lightning
- All of these
- Since all the mentioned processes (industries, *Rhizobium*, and lightning) can fix nitrogen, the correct answer is "All of these."

4. **Conclusion:**
- Therefore, nitrogen fixation can be done by industries, *Rhizobium*, lightning, and all of these.

**Final Answer:** Nitrogen fixation can be done by industries, *Rhizobium*, lightning, and all of these.

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