NEET BIOLOGY

Detailed explanation-1: -Rhodospirillum is a free-living nitrogen-fixing bacteria. Because it is a facultative anaerobe, it can use alcoholic fermentation in low-oxygen environments or aerobic respiration in high-oxygen environments.

Detailed explanation-2: -Rhodospirillum is a gram negative purple nonsulfur bacteria generally pink in colour. It is the facultative anaerobe. It is free-living bacteria which helps in nitrogen fixation by converting atmospheric nitrogen into ammonia by virtue of nitrogenase enzyme in the soil.

Detailed explanation-3: -Only Rhodospirillum is anaerobic in the given options . Remaining all are aerobic.

Detailed explanation-4: -Final answer: A free living anaerobic bacterium capable of fixing nitrogen is cyanobacteria.

Detailed explanation-5: -Nitrogen Fixing Bacteria: Azotobacter, Beijerinckia and Clostridium (anaerobic) are saprophytic bacteria that perform organic processes. Desulfovibrio is chemotrophic nitrogen fixing bacteria. Rhodopseudomonas, Rhodospirillum and Chromatium are nitrogen fixing photoautotrophic bacteria.