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

Which element is required for the activation of nitrogenase enzymes?

We find that $Rhizobium$ forms nodules on the roots of leguminous plants. Also,$Frankia$,another microbe,forms nitrogen-fixing nodules on the roots of the non-leguminous plant $Alnus$. Can we artificially induce the property of nitrogen fixation in a plant,whether leguminous or non-leguminous?

Provide definitions/explanations for the following terms:
$(1)$ Biological Nitrogen Fixation
$(2)$ Root Nodules

$Azotobacter$ and $Clostridium$ are nitrogen-fixing bacteria and are found in:

For its action,nitrogenase requires