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

Ureides are preferred forms for storage and transport of nitrogen in

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

Which of the following bacteria are free-living nitrogen fixers?
$(i)$ $Pseudomonas$ $(ii)$ $Azospirillum$
$(iii)$ $Azotobacter$ $(iv)$ $Nostoc$

Name the most crucial enzyme found in root nodules for $N_2$ fixation. Does it require a special pink-coloured pigment for its functioning? Elaborate.

How many $ATP$ molecules are required for the production of each $NH_3$ molecule during biological nitrogen fixation?