The bacteria which are associated with some plant roots and fix atmosphere nitrogen are:-

Options

A. Azotobacter
B. E.coli
C. Rhizobium
D. Pseudomonas

Answer

### Step-by-Step Solution:

1. **Understanding the Question**: The question asks for the type of bacteria that are associated with plant roots and are capable of fixing atmospheric nitrogen.

2. **Identifying the Options**: The options provided are:
- Zootobacter
- E. coli
- Rhizobium
- Pseudomonas

3. **Analyzing Each Option**:
- **Zootobacter**: While it plays a role in the nitrogen cycle, it does not form a symbiotic relationship with plant roots.
- **E. coli**: This bacterium is primarily found in the intestines of warm-blooded organisms and is not involved in nitrogen fixation.
- **Pseudomonas**: Although some species can be involved in nitrogen cycling, they do not form symbiotic relationships with plant roots for nitrogen fixation.
- **Rhizobium**: This is a genus of gram-negative bacteria that forms a symbiotic relationship with the roots of legume plants. It colonizes root nodules and converts atmospheric nitrogen into ammonia, which the plant can use.

4. **Conclusion**: Based on the analysis, the bacteria that are associated with some plant roots and fix atmospheric nitrogen is **Rhizobium**.

### Final Answer:
The correct answer is **Rhizobium**.

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