$Azotobacter$ and $Bacillus \text{ } polymyxa$ are:

Categorize the following nitrogen-fixing microorganisms into symbiotic and free-living types:
$I-$ Rhizobium
$II-$ Azotobacter
$III-$ Beijerinckia
$IV-$ Rhodospirillum
$V-$ Frankia
$VI-$ Bacillus
$VII-$ Anabaena (free-living)
$VIII-$ Nostoc (symbiotic)
Select the correct grouping for (Symbiotic) and (Free-living) respectively.

Which of the following is a non-symbiotic nitrogen-fixing prokaryote?

Identify the non-leguminous plants that form nodules to fix nitrogen.

Cobalt is . . .

Which of the following red pigments is present in the root nodules of leguminous plants?