Q.Which of the following is a free living nitrogen fixing bacteria?

Nitrogen fixation is the conversion of chemically inert atmospheric nitrogen (N2, its two atoms joined by a strong triple covalent bond) into ammonia, the form in which nitrogen becomes usable by living organisms. It proceeds by two broad routes: non-biological fixation, which needs no organism (industrial chemical fixation, and natural fixation by the electrical energy of lightning), and biological fixation, carried out by bacteria and cyanobacteria either symbiotically, in partnership with a plant host, or non-symbiotically, as free-living organisms in soil or water. Nitrogen fixation matters be …