Dentrification is carried out by

Options

A. Pseudomonas
B. Nitrobacter
C. Nitrosomonas
D. Nitrococcus

Answer

### Step-by-Step Solution:

1. **Understanding Denitrification**:
- Denitrification is the process where fixed nitrogen compounds (like nitrates) are converted back into nitrogen gas (N₂), which is released into the atmosphere. This process is crucial for the nitrogen cycle as it helps maintain the balance of nitrogen in the environment.

2. **Identifying the Options**:
- The options provided are:
1. Pseudomonas
2. Nitrobacter
3. Nitrosomonas
4. Nitrococcus

3. **Analyzing Each Option**:
- **Pseudomonas**: This genus includes species like Pseudomonas denitrificans, which are known to carry out denitrification.
- **Nitrobacter**: This bacterium is involved in nitrification, specifically in converting nitrites to nitrates.
- **Nitrosomonas**: This bacterium is also involved in nitrification, converting ammonia to nitrites.
- **Nitrococcus**: Similar to Nitrobacter and Nitrosomonas, Nitrococcus is involved in the nitrification process.

4. **Conclusion**:
- Based on the analysis, the primary bacteria responsible for denitrification is **Pseudomonas**. Therefore, the correct answer to the question "Dentrification is carried out by" is **Pseudomonas**.

### Final Answer:
**Pseudomonas**

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