Which of the following is a nitrogen fixing bacterium present in legume roots?

Rhizobia is “the group of soil bacteria that infect the roots of legumes to form root nodules”. Rhizobia are found in the soil and after infection, they produce nodules in the legume where they fix nitrogen gas (N₂) from the atmosphere, turning it into a more readily useful form of nitrogen (N). From here, the nitrogen is exported from the nodules and used for growth in the legume. Once the legume dies, the nodule breaks down and releases the rhizobia back into the soil where they can live individually or reinfect a new legume host.