Free living nitrogen-fixing bacteria are found in-

Options

A. Air
B. Soil
C. Root nodules
D. None of the above

Answer

**Step-by-Step Solution:**

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

2. **Identifying Free Living Nitrogen-Fixing Bacteria:**
- Free living nitrogen-fixing bacteria are those that do not require a host plant to fix nitrogen. They can exist independently in the environment.

3. **Analyzing the Options:**
- The options provided are:
- A) Air
- B) Soil
- C) Root nodules
- D) None of the above

4. **Evaluating Each Option:**
- **Air:** While the atmosphere contains a high percentage of nitrogen (78%), it is in an inert form and cannot be utilized by organisms directly. No nitrogen-fixing bacteria live freely in the air.
- **Soil:** This is where free living nitrogen-fixing bacteria thrive. They convert inert nitrogen into biologically active forms like ammonia. Examples include Azotobacter, Azo spirillum, and Clostridium.
- **Root Nodules:** These are specialized structures on the roots of certain plants (like legumes) that house symbiotic bacteria (e.g., Rhizobium). These bacteria fix nitrogen but are not free living.
- **None of the above:** This option is incorrect since we have identified soil as the correct answer.

5. **Conclusion:**
- The correct answer is **B) Soil**, as free living nitrogen-fixing bacteria are primarily found in the soil where they perform nitrogen fixation.