$(i)\, A3^-\rightarrow A^{2-} + e; E° = 1.5 \,V$
$(ii) \,B^{+}+ e \rightarrow B; E° = 0.5 \,V$
$(iii)\, C^{2+} + e \rightarrow C^{+}; E°= 0.5\, V$
$(iv)\, D \rightarrow D^{2+}+ 2e; E° = -1.15\, V$
$2Fe(s)\, + \,{O_2}\,(g)\, + \,4{H^ + }(aq)\, \to \,2F{e^{2 + }}(aq) + 2{H_2}O(l)\,;$ $E^o =1.67\,V$
$[Fe^{2+}] = 10^{-3}\, M$, $p(O_2) = 0.1\,atm$ અને $pH = 3$, $25\,^oC$ તાપમાને સેલ પોટેન્શિયલ .............. $\mathrm{V}$