$E_{F{e^{3 + }}/Fe}^o = 0.036V\\$ $F{e^{3 + }} + 3{e^ - } \to Fe\\$ $\therefore \Delta G_1^o = - nF{E^o}$ $= - 3F( - 0.036)\\$ $E_{F{e^{2 + }}/Fe}^o = 0.440V\\$ $F{e^{2 + }} + 2{e^ - } \to Fe;{E^o} = - 0.440V\\$ $Fe \to F{e^{2 + }} + 2{e^ - };{E^o} = 0.440V\\$ $\therefore \Delta G_2^o = - 2F(0.440)\\$ $E_{{I_2}/2{I^ - }}^o = 0.539V\\$ ${I_2} + 2{e^ - } \to 2{I^ - };{E^o} = 0.539V\\$ $2{I^ - } \to {I_2} + 2{e^ - };{E^o} = - 0.539V\\$ $\Delta G_3^o = - 2F( - 0.539)\\$ $\therefore \Delta {G^o} = 2\left[ {\Delta G_1^o + \Delta G_2^o} \right] + \Delta G_3^o\\$ $= 2\left[ {3F(0.036) - 2F(0.440)} \right] + 2F(0.539)\\$ $= - 45934 = - 45.9KJ \simeq - 46KJ$