Chemistry - Complete d-block Question with Solution | TestHub

Ionization energy, in chemistry and physics, the amount of energy required to remove an electron from an isolated atom or molecule. 

$3^{\mathrm{rd}}$ Ionisation energy:

$\mathrm{V} : 2833 \mathrm{kJ}/\mathrm{mol}$

$\mathrm{Cr}: 2990 \mathrm{kJ}/\mathrm{mol}$

$\mathrm{Mn}:3260 \mathrm{kJ}/\mathrm{mol}$

$\mathrm{Fe}:2962 \mathrm{kJ}/\mathrm{mol}$

alternative

$\mathrm{Mn}:3 {\mathrm{d}}^{5}4 {\mathrm{s}}^2$

$\mathrm{Fe}:3 {\mathrm{d}}^{6}4 {\mathrm{s}}^2$

$\mathrm{Cr}:3 {\mathrm{d}}^{5}4 {\mathrm{s}}^1$

$\mathrm{V}:3 {\mathrm{d}}^{3}4 {\mathrm{s}}^2$

So $\mathrm{Mn}$ has highest $3^{\mathrm{rd}} \mathrm{IE}$ among all the given elements due to ${\mathrm{d}}^5$configuration