Multiple choice

Which of the following is a free-living anaerobic nitrogen fixing bacteria?

  1. Clostridium

  2. Rhizobium

  3. Azotobacter

  4. Nitrobacter
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A Correct answer
Explanation

Clostridium is a free-living anaerobic nitrogen-fixing bacteria. It lives in soil and fixes nitrogen without requiring oxygen or a host plant. Rhizobium is symbiotic (requires legume host), Azotobacter is aerobic (requires oxygen), and Nitrobacter is a nitrifying bacteria that converts nitrite to nitrate but does not fix nitrogen.

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