Identify the bacteria which can fix atmospheric nitrogen and are free-living in the soil.
(A) Azotobacter
(B) Rhizobium
(C) Azospirillum
(D) Anabaena
Choose the correct answer from the options given below:
Answer & explanation
Correct answer: option 1
The correct answer is Option (1) → (A) and (C) only
Some bacteria fix atmospheric nitrogen, which means they turn it into forms that plants can use. They differ in how they live. Rhizobium is symbiotic. It lives in the root nodules of leguminous plants. Other bacteria fix nitrogen while they are free-living in the soil, and this adds to the nitrogen content of the soil.
(A) Azotobacter — Correct. NCERT gives it as a free-living nitrogen fixer of the soil.
(B) Rhizobium — Incorrect. It fixes nitrogen only in symbiosis, in the root nodules of leguminous plants.
(C) Azospirillum — Correct. NCERT gives it as a free-living nitrogen fixer of the soil.
(D) Anabaena — Incorrect. It is a cyanobacterium, and NCERT treats cyanobacteria as a separate group of biofertilisers. They live in water and on land and are important in paddy fields. NCERT names only Azospirillum and Azotobacter as the free-living nitrogen fixers of the soil.
Note: A similar question was also asked in CUET (UG) 2026 on 07-06-2026 (Slot 2) and on 21-05-2026 (Slot 1).
NCERT Extract:
Microbes as Biofertilisers – …
