Bacteria which convert the nitrogen of the air to nitrogenous compounds are called

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.

Which one of the following produces nitrogen-fixing nodules on the roots of $Alnus$?

Explain the process/mechanism of biological nitrogen fixation.

Which of the following genes is responsible for biological nitrogen fixation?

Which of the following is an example of a free-living and anaerobic $N_2$-fixing bacterium?