Mark the incorrect option (w.r.t. nitrifying bacteria)
(a) Nitrococcus
(b) Leptothrix
(c) Nitrobacter
(d) Nitrocystis

Options

A. Nitrococcus
B. Leptothrix
C. Nitrobacter
D. Nitrocystis

Answer

To solve the question of identifying the incorrect option with respect to nitrifying bacteria, we can follow these steps:

### Step-by-Step Solution:

1. **Understand Nitrifying Bacteria**: Nitrifying bacteria are a group of bacteria that play a crucial role in the nitrogen cycle, specifically in the process of nitrification. They convert ammonia (NH₃) or ammonium (NH₄⁺) into nitrites (NO₂⁻) and then into nitrates (NO₃⁻).

2. **Identify Common Nitrifying Bacteria**: Some well-known nitrifying bacteria include:
- **Nitrosomonas**: Converts ammonia to nitrite.
- **Nitrobacter**: Converts nitrite to nitrate.
- **Nitrococcus**: Also involved in the nitrification process.
- **Nitrocystis**: Another nitrifying bacterium.

3. **Analyze the Options**:
- **(a) Nitrococcus**: This is a nitrifying bacterium.
- **(b) Leptothrix**: This is not a nitrifying bacterium; it is known for its role in iron oxidation and not in nitrification.
- **(c) Nitrobacter**: This is a nitrifying bacterium.
- **(d) Nitrocystis**: This is also a nitrifying bacterium.

4. **Identify the Incorrect Option**: Based on the analysis, **Leptothrix (option B)** is the incorrect option as it does not belong to the category of nitrifying bacteria.

### Final Answer:
The incorrect option with respect to nitrifying bacteria is **(b) Leptothrix**.

---