The enzyme responsible for atmospheric nitrogen fixation is

Which of the following organisms is a free-living,aerobic,photosynthetic nitrogen fixer?

Soil fertility can be increased by ..........

The nitrogenase enzyme found in the root nodules of legumes contains:

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

How many electrons and protons are required to fix a molecule of dinitrogen $(N_2)$ (in each)?