Redox reactions play a pivotal role in chemistry and biology. The values of standard redox potential (E°) of two half-cell reactions decided which way the reaction is expected to proceed. A simple example is a Daniel cell in which zinc goes into solution and copper gets deposited. Given below are a set of half-cell reactions (acidic medium) along with their E⁰ values (with respect to normal hydrogen electrode) Using this data : ${\mathrm{I}}_2+2e^{-}\to 2{\mathrm{I}}^{-},{\mathrm{E}}^0=0.54;{\mathrm{Cl}}_2+2e^{-}\to 2{\mathrm{Cl}}^{-},E=1.36\mathrm{V}$
${\mathrm{Mn}}^{3+}+{\mathrm{e}}^{-}\to {\mathrm{Mn}}^{2+},{\mathrm{E}}^0=1.50;{\mathrm{Fe}}^{3+}+{\mathrm{e}}^{-}\to {\mathrm{Fe}}^{2+},\mathrm{E}=0.77\mathrm{V};{\mathrm{O}}_2+4{\mathrm{H}}^{+}+4{\mathrm{e}}^{-}\to 2{\mathrm{H}}_2\mathrm{O},{\mathrm{E}}^{\circ }=1.23$