Which of the following is a free living soil nitrogen fixing bacteria?
Answer & explanation
Correct answer: option 3
The correct answer is Option (3) → Azospirillum
Option (1) Rhizobium — Incorrect. Rhizobium fixes nitrogen in root nodules.
Option (2) Glomus — Incorrect. Glomus is a mycorrhizal fungus.
Option (3) Azospirillum — Correct. Azospirillum fixes nitrogen while free-living in soil.
Option (4) Oscillatoria — Incorrect. Oscillatoria is a cyanobacterium of paddy fields, not a soil bacterium.
Note: A similar question was also asked in CUET (UG) 2026 on 30-05-2026 (Slot 2) and on 29-05-2026 (Slot 2), and in CUET (UG) 2025 on 29-05-2025 (Slot 1), on 26-05-2025 (Slot 2) and on 22-05-2025 (Slot 2).
NCERT Extract:
Microbes as Biofertilisers – “… You have studied about the nodules on the roots of leguminous plants formed by the symbiotic association of Rhizobium. These bacteria fix atmospheric nitrogen into organic forms, which is used by the plant as nutrient. Other bacteria can fix atmospheric nitrogen while free-living in the soil (examples Azospirillum and Azotobacter), thus enriching the nitrogen content of the soil.”