Rhizobium
Nostoc
Azotobacter
Nitrobacter
Answer is Right!
Answer is Wrong!
The correct answer is A. Rhizobium.
Rhizobium is a genus of bacteria that forms symbiotic relationships with legumes. These bacteria live in root nodules and fix atmospheric nitrogen into ammonia, which the plant can use to grow.
Nostoc is a genus of cyanobacteria that can fix nitrogen. However, it does not form symbiotic relationships with plants.
Azotobacter is a genus of bacteria that can fix nitrogen. However, it is not as efficient at nitrogen fixation as Rhizobium.
Nitrobacter is a genus of bacteria that oxidizes ammonia to nitrite. It is not involved in nitrogen fixation.
In conclusion, Rhizobium is the only option that is a nitrogen-fixing bacterium that forms symbiotic relationships with plants.