$(i)\,F{e^{2 + }}\, + \,2{e^ - }\, \to \,Fe;$                    ${E^o}\, = \, - 0.47\,\,V;$

$(ii)\,F{e^{3 + }}\, + \,{e^ - }\, \to \,F{e^{2 + }};$          ${E^o}\, = \, + 0.77\,\,V;$

$(iii)\,F{e^{3 + }}\, + \,3{e^ - }\, \to Fe$

$(i)\,\Delta {G^o}\, = \, - nF{E^o}\, = \, - \,2\,( - 0.47)F\, = \,0.94\,F$

$(ii)\,\Delta {G^o}\, = \, - nF{E^o}\, = \, - \,1\,( + 0.77)F\, = \, - 0.77F$

$(iii)$ on adding $:\,\Delta {G^o}\, = \, + \,0.17\,F$

$\Delta {G^o}\, = \, - nF{E^o}\,{E^o}$ for

$(F{e^{3 + }} \to Fe)\, = \,\frac{{\Delta {G^o}}}{{ - nF}}\,$ $ = \,\frac{{0.17F}}{{ - 3F}}\, = \, - \,0.057\,V$