JEE Main 2013 — Chemistry Physical Chemistry

Species having the highest reduction potential i.e., tendency to undergo reduction by gain of electron. SRP value increases from left to right in the period for the d-block elements.

$${\mathrm{ M}}^{ 3+ } (aq) +1{e}^{-} \rightarrow {M}^{ 2+ } (aq)$$M3+(aq)+1e−→M2+(aq)

$$\begin{matrix}{ }_{26}{\text{Fe}}^{3+}/{\text{Fe}}^{2+}\Rightarrow & 4{\text{s}}^{0}3{\text{d}}^{5}\rightarrow 4{\text{s}}^{0}3{\text{d}}^{6} & (+0\text{.}77\text{ volt}) \\ { }_{27}{\text{Co}}^{3+}/{\text{Co}}^{2+}\Rightarrow & 4{\text{s}}^{0}3{\text{d}}^{6}\rightarrow 4{\text{s}}^{0}3{\text{d}}^{7} & (+1\text{.}97\text{ volt}) \\ { }_{24}{\text{Cr}}^{3+}/{\text{Cr}}^{2+} & 4{\text{s}}^{0}3{\text{d}}^{3}\rightarrow 4{\text{s}}^{0}3{\text{d}}^{4} & (-0\text{.}4\text{ volt}) \\ { }_{25}{\text{Mn}}^{3+}/{\text{Mn}}^{2+} & 4{\text{s}}^{0}3{\text{d}}^{4}\rightarrow 4{\text{s}}^{0}3{\text{d}}^{5} & (+1\text{.}57\text{ volt})\end{matrix}$$26​Fe3+/Fe2+⇒27​Co3+/Co2+⇒24​Cr3+/Cr2+25​Mn3+/Mn2+​4s03d5→4s03d64s03d6→4s03d74s03d3→4s03d44s03d4→4s03d5​(+0.77 volt)(+1.97 volt)(−0.4 volt)(+1.57 volt)​

Highest reduction potential means strong oxidising agent, i.e. undergoing reduction ${\mathrm{Co}}^{3+}+1{e}^{-}\rightarrow {\mathrm{Co}}^{2+}$Co3++1e−→Co2+.