The enzyme responsible for atmospheric nitrogen fixation is

$nif$ genes occur in

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

The enzyme nitrogenase functions under $............$ conditions.

The function of leghaemoglobin during $N_2$-fixation is

$A -$ The enzyme nitrogenase is highly sensitive to molecular oxygen.
$R -$ To protect nitrogenase enzymes,the nodule contains an oxygen scavenger called leghaemoglobin.