Study the following in nitrogen cycle and identify A and B
`NH_3 overset((A))to NO_2^(-) overset(B)to NO_3^(-)`

Options

A. A-Nitrosomonas, B-Nitrobactor
B. A-Nitrobactor, B-Nitrobactor
C. A-Nitrobactor, B-Nitrosomonas
D. A-Thiobacillus, B-Nitrobacter

Answer

To solve the question regarding the nitrogen cycle and identify A and B in the conversion of ammonia (NH₃) to nitrite (NO₂⁻) and then to nitrate (NO₃⁻), we will follow these steps:

### Step-by-Step Solution:

1. **Understand the Nitrogen Cycle**: The nitrogen cycle involves various processes that convert nitrogen from one form to another in the environment. Key processes include nitrogen fixation, nitrification, denitrification, and ammonification.

2. **Identify the Process of Nitrification**: Nitrification is the process where ammonia (NH₃) is converted into nitrite (NO₂⁻) and then into nitrate (NO₃⁻). This process is carried out by specific bacteria.

3. **Identify the Bacteria Involved**:
- **Conversion of NH₃ to NO₂⁻**: The first step in nitrification involves the conversion of ammonia to nitrite. This step is carried out by a type of bacteria known as **Nitrosomonas**.
- **Conversion of NO₂⁻ to NO₃⁻**: The second step involves the conversion of nitrite to nitrate. This step is performed by another type of bacteria known as **Nitrobacter**.

4. **Assign Labels A and B**:
- **A** corresponds to the bacteria that convert ammonia (NH₃) to nitrite (NO₂⁻), which is **Nitrosomonas**.
- **B** corresponds to the bacteria that convert nitrite (NO₂⁻) to nitrate (NO₃⁻), which is **Nitrobacter**.

5. **Final Answer**: Therefore, A is **Nitrosomonas** and B is **Nitrobacter**.

### Summary:
- A: Nitrosomonas (converts NH₃ to NO₂⁻)
- B: Nitrobacter (converts NO₂⁻ to NO₃⁻)