Which of the following free living soil microorganisms are used as biofertilisers?
(A) Anabaena
(B) Azospirillum
(C) Rhizobium
(D) Azotobacter
Choose the correct answer from the options given below:
Answer & explanation
Correct answer: option 4
The correct answer is Option (4) → (B) and (D) only
Biofertilisers are organisms that enrich the nutrient content of the soil.
(A) Anabaena Incorrect. Anabaena is a cyanobacterium (blue-green alga) that fixes nitrogen in aquatic habitats and paddy fields. The book lists it with Nostoc and Oscillatoria under cyanobacteria, not with the free-living soil bacteria.
(B) Azospirillum Correct. A free-living nitrogen-fixing bacterium of the soil.
(C) Rhizobium Incorrect. Rhizobium is symbiotic. It lives in the root nodules of leguminous plants and fixes nitrogen there.
(D) Azotobacter Correct. Another free-living soil bacterium that fixes atmospheric nitrogen and so enriches the nitrogen content of the soil.
Note: The same question was also asked in CUET (UG) 2025 on 30-05-2025 (Slot 1).
NCERT Extract:
Microbes as Biofertilisers – …
