Which one is a non-symbiotic nitrogen fixer?

$A-$ The microbe $Frankia$ produces nitrogen-fixing nodules on the roots of non-leguminous plants.
$R-$ Both $Rhizobium$ and $Frankia$ are free-living in soil,but as symbionts,can fix atmospheric nitrogen.

The most active nitrogen-fixing blue-green alga in rice fields is:

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

Which of the following is responsible for atmospheric nitrogen fixation?

Which of the following organisms fixes atmospheric nitrogen in a free-living state?