Chemistry - Electrochemistry Question with Solution | TestHub

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.
$M^{3+}(aq)+1e^{-}\to M^{2+}(aq)$
$\begin{array}{ccc}{}_{26}{\text{Fe}}^{3+}/{\text{Fe}}^{2+}\Rightarrow & 4{\text{s}}^{0}3{\text{d}}^5\to 4{\text{s}}^{0}3{\text{d}}^6& \left(+0\text{.}77\text{ volt}\right)\\ {}_{27}{\text{Co}}^{3+}/{\text{Co}}^{2+}\Rightarrow & 4{\text{s}}^{0}3{\text{d}}^6\to 4{\text{s}}^{0}3{\text{d}}^7& \left(+1\text{.}97\text{ volt}\right)\\ {}_{24}{\text{Cr}}^{3+}/{\text{Cr}}^{2+}& 4{\text{s}}^{0}3{\text{d}}^3\to 4{\text{s}}^{0}3{\text{d}}^4& \left(-0\text{.}4\text{ volt}\right)\\ {}_{25}{\text{Mn}}^{3+}/{\text{Mn}}^{2+}& 4{\text{s}}^{0}3{\text{d}}^4\to 4{\text{s}}^{0}3{\text{d}}^5& \left(+1\text{.}57\text{ volt}\right)\end{array}$

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