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One of the free-living anaerobic nitrogen-fixers is
A
$Azotobacter$
B
$Beijerinckia$
C
$Rhodospirillum$
D
$Rhizobium$
Detailed Solution
Free-living nitrogen-fixing microbes may be aerobic or anaerobic.
$Azotobacter$ and $Beijerinckia$ are free-living aerobic nitrogen fixers.
$Rhodospirillum$ is a free-living anaerobic nitrogen fixer; $Bacillus$ is also free-living.
$Rhizobium$ is a symbiotic nitrogen fixer that lives in the root nodules of legumes.
Hence the free-living anaerobic nitrogen fixer is $Rhodospirillum$.
$Azotobacter$ and $Beijerinckia$ are free-living aerobic nitrogen fixers.
$Rhodospirillum$ is a free-living anaerobic nitrogen fixer; $Bacillus$ is also free-living.
$Rhizobium$ is a symbiotic nitrogen fixer that lives in the root nodules of legumes.
Hence the free-living anaerobic nitrogen fixer is $Rhodospirillum$.