Which of the following is a non-symbiotic nitrogen fixing aerobic bacteria?

Correct option is C

The correct answer is (c) Azotobacter.
Azotobacter is a free-living, non-symbiotic nitrogen-fixing bacterium that functions in aerobic conditions.
Information Booster:
• Clostridium and Frankia are anaerobic or symbiotic nitrogen-fixers.
• Rhizobium is a nitrogen-fixing bacterium that forms symbiotic relationships with legumes.