which of the following pairs serve as biofertilizers?

Options

A. Albugo and lichen
B. Frankia and Nostoc
C. Pseudomans and E.Coli
D. Spiroyra and mucor

Answer

To determine which pairs serve as biofertilizers, we need to analyze each option provided in the question.

### Step-by-Step Solution:

1. **Understanding Biofertilizers**:
- Biofertilizers are substances that contain living microorganisms which promote plant growth by increasing the availability of nutrients to the host plant. They enhance soil fertility and are often used in sustainable agriculture.

2. **Analyzing the Options**:
- **Option 1: Albugo and Lichen**:
- Albugo is a genus of fungi that causes diseases in plants, while lichens are symbiotic associations between fungi and algae or cyanobacteria. Neither of these is primarily used as a biofertilizer.

- **Option 2: Francia and Nostoc**:
- Francia is a nitrogen-fixing bacteria that forms symbiotic relationships with plants, particularly in root nodules. Nostoc is a type of blue-green algae (cyanobacteria) that also fixes nitrogen. Both of these microorganisms contribute to soil fertility and are used as biofertilizers.

- **Option 3: Judomonas and Escherichia coli**:
- Judomonas is not a well-known organism in the context of biofertilizers, and Escherichia coli is a bacterium commonly found in the intestines of humans and animals, not used as a biofertilizer.

- **Option 4: Spirogyra and Mucus**:
- Spirogyra is a green algae, but it is not typically used as a biofertilizer. Mucus does not refer to a specific organism that would act as a biofertilizer.

3. **Conclusion**:
- After analyzing all the options, the pair that serves as biofertilizers is **Francia and Nostoc**. They both play significant roles in nitrogen fixation, enhancing soil fertility.

### Final Answer:
The correct answer is **Option 2: Francia and Nostoc**.

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