How does root nodule form in leguminous plants?

It contains bacteria that fix nitrogen in the soil. This provides this vital element not only for the legume but also other plants in the vicinity

Nitrogen fixing bacteria. They convert nitrogen in the iar into a form that the plant can use.

Bacteria is found in root nodules :)

they have got a root nodule

the root nodules of plant help in absorbing many nutrients essential for the plant...