How many nitrogen molecules are required for the synthesis of 8 ammonia molecules during nitrogen fixation?

${\mathrm{N}}_2+8{\mathrm{e}}^{-}+8{\mathrm{H}}^{+}+16\mathrm{ATP}\to 2{\mathrm{NH}}_3+{\mathrm{H}}_2+16\mathrm{ADP}+16{\mathrm{P}}_1$

1 molecule of nitrogen is used to produce 2 molecules of ammonia. Therefore, to produce 8 molecules of nitrogen there is the requirement of 4 molecules of nitrogen.