Nitrogen fixing bacteria is/are
A. Azotobacter B. Rhizobium C. Bacillus D. Azospirillum E. Pseudomonas
Choose the correct answer from the options given below

Correct option is A

Biological nitrogen fixation is the process by which atmospheric nitrogen is converted into usable forms by certain microorganisms. Azotobacter is a free-living nitrogen fixing bacterium that fixes nitrogen independently in aerobic soil conditions. Rhizobium fixes nitrogen symbiotically in association with leguminous crops by forming root nodules. Azospirillum fixes nitrogen under associative symbiosis with cereal and grass crops.
Information booster: Biological nitrogen fixation plays a major role in maintaining soil fertility and reducing dependence on chemical fertilizers. Rhizobium is crop-specific and forms effective nodules only with compatible legume hosts. Azotobacter is aerobic in nature, while Azospirillum is microaerophilic. Use of nitrogen fixing biofertilizers supports sustainable and environmentally safe agriculture.
Why other options are incorrect: (b) Bacillus species are mainly decomposers and not true nitrogen fixing bacteria. (c) Pseudomonas does not fix atmospheric nitrogen biologically. (d) This option is incorrect because not all the listed bacteria fix nitrogen.