What type of conditions are created by leghaemoglobin in the root nodule of a legume?

The free-living anaerobic nitrogen-fixing bacterium is . . . . . . .

Which mineral plays a vital role in nitrogen fixation?

The biological process carried out by $Rhizobium$ is called:

The chemical fertilizer required for better rhizobial nitrogen fixation is

Analogy type questions:
$(1)$ Reduction of nitrogen to ammonia : Biological nitrogen fixation : Nitrogenase : ........
$(2)$ Free-living bacteria : Rhodospirillum : Free-living blue-green algae : ........