`N_(2)`-fixing blue-green alga Anabaena which is extensively used in rice cultivation, forms symbiotic association with

Options

A. Cycas roots
B. Azolla
C. Anthoceros
D. Alnus

Explanation

To solve the question regarding the nitrogen-fixing blue-green alga Anabaena and its symbiotic association, we can follow these steps:

### Step-by-Step Solution:

1. **Understanding the Organisms**:
- Anabaena is a type of blue-green algae (also known as cyanobacteria) that has the ability to fix atmospheric nitrogen.
- It is important in agriculture, particularly in rice cultivation, due to its role in enhancing soil fertility.

2. **Identifying Symbiotic Relationships**:
- A symbiotic relationship is a close interaction between two different organisms, where both benefit from the association.
- In this context, we need to identify which organism forms a symbiotic relationship with Anabaena.

3. **Recognizing the Partner**:
- Anabaena forms a well-known symbiotic association with Azolla, which is a water fern (a type of pteridophyte).
- In this relationship, Anabaena provides fixed nitrogen to Azolla, while Azolla offers a suitable habitat and nutrients to Anabaena.

4. **Conclusion**:
- Given the information, the correct answer to the question is that Anabaena forms a symbiotic association with Azolla.

### Final Answer:
Anabaena forms a symbiotic association with **Azolla**.

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