The bacterium capable of anaerobic `N_(2)` fixation is known as

Options

A. Clostridium
B. Bacillus
C. Azotobacter
D. Rhizobium

Answer

To answer the question, "The bacterium capable of anaerobic N2 fixation is known as," we can follow these steps:

### Step-by-Step Solution:

1. **Understanding Nitrogen Fixation**:
- Nitrogen fixation is the process by which atmospheric nitrogen (N2) is converted into ammonia (NH3), which plants can use. This process is essential because plants cannot directly utilize atmospheric nitrogen.

2. **Identifying Types of Nitrogen Fixation**:
- There are two main types of nitrogen fixation: anaerobic (occurring in the absence of oxygen) and aerobic (occurring in the presence of oxygen).

3. **Recognizing Anaerobic Nitrogen-Fixing Bacteria**:
- Anaerobic nitrogen-fixing bacteria thrive in environments without oxygen. An example of such a bacterium is **Clostridium**.

4. **Distinguishing from Aerobic Nitrogen-Fixing Bacteria**:
- It's important to differentiate between anaerobic and aerobic nitrogen-fixing bacteria. For instance, **Azotobacter** and **Rhizobium** are examples of aerobic nitrogen-fixing bacteria, as they require oxygen for their nitrogen-fixing processes.

5. **Final Answer**:
- Therefore, the bacterium capable of anaerobic nitrogen fixation is **Clostridium**.

### Final Answer:
The bacterium capable of anaerobic N2 fixation is known as **Clostridium**.