Correct option (c) Frankia
Explanation :
Nitrogen is the most critical element. Certain non-leguminous plants also form nodules to fix nitrogen. The best known example in temperate region is alder (Alnus so). The bacteria involved in nodule formation is an Actinomycetes the Frankia Clostridium is anaerobic, saprotrophic free-living nitrogen fixing bacteria.
Bradyrhizobium sp are symbiont in plants of Paraspania and soyabean.
The Azorhizobium froms both stem and root nodules in Sasbaina (aquatic plant).
