Select the mismatch :

Options

A. Frankia - Alnus
B. Rhodospirillum - Mycorrhiza
C. Anabaena - Nitrogen fixed
D. Rhizobium - Alfalfa

Answer

To solve the question "Select the mismatch," we need to analyze each option provided and determine which one does not correctly match the terms or concepts associated with them.

### Step-by-Step Solution:

1. **Identify the Options:**
- Option A: Frankia - Nitrogen fixer
- Option B: Rhodospirillum - Mycorrhizae
- Option C: Azolla - Nitrogen fixed
- Option D: Rhizobium - Alfalfa

2. **Analyze Option A: Frankia**
- Frankia is a genus of bacteria known for its ability to fix nitrogen. It forms symbiotic relationships with certain plants, particularly actinorhizal plants. This option is correctly matched.

3. **Analyze Option B: Rhodospirillum - Mycorrhizae**
- Rhodospirillum is a genus of bacteria that is known to be an anaerobic nitrogen fixer. Mycorrhizae, on the other hand, refers to a symbiotic association between fungi and the roots of higher plants. Since Rhodospirillum does not form a mycorrhizal relationship, this option is a mismatch.

4. **Analyze Option C: Azolla - Nitrogen fixed**
- Azolla is a water fern that has a symbiotic relationship with nitrogen-fixing cyanobacteria (Anabaena). This relationship allows Azolla to fix nitrogen, making this option correctly matched.

5. **Analyze Option D: Rhizobium - Alfalfa**
- Rhizobium is a genus of bacteria that forms symbiotic relationships with legumes, including alfalfa, to fix nitrogen. This option is also correctly matched.

6. **Conclusion:**
- Based on the analysis, the mismatch is found in **Option B: Rhodospirillum - Mycorrhizae**. Rhodospirillum is a free-living nitrogen fixer and does not form mycorrhizal associations.

### Final Answer:
The mismatch is **Option B: Rhodospirillum - Mycorrhizae**.