In nitrification, ammonia is first oxidised to nitrite by

Options

A. Nitrosomonas and Nitrococcus
B. Nitrosomonas and Nitrobactor
C. Pseudomonas and Nitrococcus
D. Pseudomonas and Thiobacillus

Answer

**Step-by-Step Solution:**

1. **Understanding Nitrification**:
- Nitrification is a biological process in which ammonia (NH₃) is converted into nitrite (NO₂⁻) and then into nitrate (NO₃⁻) by specific bacteria in the soil.

2. **Identifying the First Step**:
- The first step of nitrification involves the oxidation of ammonia to nitrite. This is a crucial step in the nitrogen cycle.

3. **Bacteria Involved**:
- The bacteria responsible for the oxidation of ammonia to nitrite are primarily from the genus **Nitrosomonas**.

4. **Process of Oxidation**:
- The chemical reaction can be summarized as:
\[ 2NH₄^+ + 3O₂ \rightarrow 2NO₂^- + 4H^+ + 2H₂O \]
- Here, ammonium ions (NH₄⁺) are oxidized to nitrite (NO₂⁻) with the help of Nitrosomonas.

5. **Conclusion**:
- Therefore, in nitrification, ammonia is first oxidized to nitrite by **Nitrosomonas**.

**Final Answer**: Nitrosomonas

---