${\mathrm{N}}_2+8{\mathrm{e}}^{-}+8{\mathrm{H}}^{+}+16\mathrm{ATP}\to 2{\mathrm{NH}}_3+{\mathrm{H}}_2+16\mathrm{ADP}+16\mathrm{Pi}$
The above equation refers to

Correct option is 3 Nitrogen fixation

Nitrogen fixation is the conversion of inert atmospheric nitrogen into utilisable compounds of nitrogen like nitrate, ammonia and amino acids. Nitrogen fixation can be biological or a biological. In symbiotic nitrogen fixation, the free molecules of gaseous nitrogen are converted into ammonia using ATP and electrons and hydrogen from the host plant. The equation represents the process of biological nitrogen fixation and the enzyme catalyzing this reaction is nitrogenase.

So, the correct answer is option 3