The most famous nitrogen-fixing bacterium/biofertilizer is:

The process of nitrogen fixation by $Rhizobium$ is stimulated by the presence of which of the following?

Which of the following are free-living nitrogen-fixing bacteria?

The function of leghemoglobin present in the root nodules of leguminous plants is to ........

$A$ farmer adds Azotobacter culture to soil before sowing maize. Which mineral element is being replenished?

Choose the incorrect pair$(s)$:
$(I)$ Free-living nitrogen-fixing aerobic microbes - Beijerinckia
$(II)$ Rhodospirillum - Aerobic microbes
$(III)$ Bacillus - Free-living
$(IV)$ Cyanobacteria - Anabaena and Azotobacter