Hint: The legume forms a symbiotic relationship with the nitrogen-fixing soil bacteria called Rhizobium. The association between the bacteria and legume forms root nodules in which the bacterium houses which converts atmospheric nitrogen into ammonia which is utilised by the plant.
To solve this question, we must know about the leguminous plant which forms association with Rhizobium and Azorhizobium.
The leguminous plants of the pea family form symbiotic association with Rhizobium. These bacteria have the ability to fix atmospheric nitrogen and convert it into nitrates, ammonia and nitrite. These can be directly used by the plants.
Let us discuss the options given.
Crotalaria juncea- It is a tropical Asian plant belonging to the pea family. It forms a symbiotic relation with Arbuscular Mycorrhizal Fungi. This plant is used as a biofuel and also is important for phytoremediation of copper in soil.
Sesbania aculeata It is a small tree of genus Sesbania. It belongs to the pea family. It enhances the soil fertility due to the presence of Rhizobia.
Sesbania rostrata- It is a semi aquatic plant from the legume family. It forms a symbiotic relation with both Rhizobium and Azorhizobium.
Cyamopsis tetragonoloba- This plant of the pea family has root nodules with Rhizobium and helps fixing nitrogen and improving soil fertility.
Hence, the correct answer is option (C)
Note: Azorhizobium genus is a gram negative soil bacterium. They can fix nitrogen in a free living state. They are motile soil bacterium. It plays an important role in maintaining the biological nitrogen cycle.