Explanation

(a)
Reactions
(i) $Fe(s) \rightarrow \ {Fe}^{2 +}\ + \ {2e}^{-},\ \ \ \ \ \ E^{{^\circ}}\ = \ + \ 0.44\ V$
and ${\mathrm{\Delta}G}_{1}^{{^\circ}} = - \ {nE}^{{^\circ}}F = \ - \ 2\ \times \ 0.44\ \times \ F$
(ii)$\ {2H}^{+} + {2e}^{-} + \frac{1}{2}O_{2} \longrightarrow H_{2}O(l);\ \ \ E^{{^\circ}} = + 1.23\ V$
and ${\mathrm{\Delta}G}_{2}^{{^\circ}} = - \ 2\ \times ( + \ 1.23) \times F$
Net reaction,
$Fe\ (s) + {2H}^{+} + \frac{1}{2}O_{2}\ \rightarrow {Fe}^{2 +} + H_{2}O(l)$
${\mathrm{\Delta}G}_{3}^{{^\circ}} = \ {\mathrm{\Delta}G}_{1}^{{^\circ}}\ + \ {\mathrm{\Delta}G}_{2}^{{^\circ}}$
$= - 2 \times ( + \ 0.44)\ F + ( - \ 2 \times 1.23 \times F)$
$= - \ 0.88\ F\ \times - \ 2.46\ F = - \ 3.34\ F$
$= - \ 3.34 \times 96500\ J$
$= - 322.31\ kJ = - \ 322\ kJ\$