Which of the following is a nitrogen-fixing organism?

Options

A. Some BGA
B. Rhizobium
C. Both (1) and (2)
D. Aspergillus

Answer

To determine which of the following is a nitrogen-fixing organism, we need to analyze the options provided: some BGA (blue-green algae), Rhizobium, both 1 and 2, or Aspergillus.

### Step-by-Step Solution:

1. **Understanding Nitrogen Fixation**:
- Nitrogen fixation is the process by which certain organisms convert atmospheric nitrogen (N₂) into ammonia (NH₃), which is a form that plants can use for growth.

2. **Analyzing the Options**:
- **Option 1: Some BGA (Blue-Green Algae)**:
- Blue-green algae, also known as cyanobacteria, are capable of fixing nitrogen. They can be free-living or form symbiotic relationships with other organisms. Therefore, some BGA can be considered nitrogen-fixing organisms.

- **Option 2: Rhizobium**:
- Rhizobium is a group of soil bacteria that specifically infect the roots of leguminous plants, forming root nodules where nitrogen fixation occurs. They are well-known nitrogen-fixing organisms.

- **Option 3: Both 1 and 2**:
- Since both BGA and Rhizobium are nitrogen-fixing organisms, this option is also valid.

- **Option 4: Aspergillus**:
- Aspergillus is a genus of filamentous fungi, commonly known as molds. There is no substantial evidence that Aspergillus contributes to nitrogen fixation.

3. **Conclusion**:
- Based on the analysis, both BGA (blue-green algae) and Rhizobium are nitrogen-fixing organisms. Therefore, the correct answer is **both 1 and 2**.

### Final Answer:
**Both 1 and 2 (Some BGA and Rhizobium) are nitrogen-fixing organisms.**

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