Nitrogen fixing organism which can be free as well as symbiotic is

Options

A. Anabaena
B. Azotobacter
C. Liverworts
D. Mossess.

Answer

To solve the question about nitrogen-fixing organisms that can exist both freely and in a symbiotic relationship, we can follow these steps:

### Step-by-Step Solution:

1. **Understand Nitrogen Fixation**:
- Nitrogen fixation is the process by which nitrogen in the atmosphere is converted into ammonia or related compounds in soil and water. This is essential for plants as they cannot use atmospheric nitrogen directly.

2. **Identify Types of Nitrogen-Fixing Organisms**:
- There are two main types of nitrogen-fixing organisms:
- **Free-living organisms**: These organisms can fix nitrogen independently in the soil or water.
- **Symbiotic organisms**: These organisms form a mutualistic relationship with plants, where they fix nitrogen in exchange for carbohydrates and a suitable environment.

3. **Review the Options Provided**:
- The options given are:
- A) Anabena
- B) Azobacter
- C) Liverworts
- D) Mosses

4. **Evaluate Each Option**:
- **Anabena**: This is a cyanobacterium that can fix nitrogen but is primarily known for its symbiotic relationships with certain plants.
- **Azobacter**: This is a free-living nitrogen-fixing bacterium that can also be found in association with plants, making it both free-living and symbiotic.
- **Liverworts**: These are non-vascular plants and do not fix nitrogen themselves.
- **Mosses**: Similar to liverworts, mosses do not fix nitrogen.

5. **Determine the Correct Answer**:
- Based on the evaluation, **Azobacter** is the only organism that can exist both freely and in a symbiotic relationship. Therefore, the correct answer is **B) Azobacter**.

### Final Answer:
The nitrogen-fixing organism that can be free as well as symbiotic is **Azobacter**.