Chemistry - Complete d-block Question with Solution | TestHub

The general trend observed in the second ionisation enthalpy of $3\mathrm{d}-$series elements is that as we move from left to right in the period, the ionisation energy increases. But, $\mathrm{Cr}$ and $\mathrm{Zn}$ are exceptions to this trend. The value of second ionisation energy for $\mathrm{Cr}$ is more than $\mathrm{Mn}$. This can be explained based on the electronic configuration of their ${\mathrm{M}}^{+}$ ions:

${}_{24}\mathrm{Cr}^{+}=\left[\mathrm{Ar}\right]3{\mathrm{d}}^5$ and ${}_{25}\mathrm{Mn}^{+}=\left[\mathrm{Ar}\right]3{\mathrm{d}}^{5}4{\mathrm{s}}^1$

${\mathrm{Cr}}^{+}$ has a stable electronic configuration because of half-filled $\mathrm{d}-$subshell. Thus removing an electron from it is difficult. Therefore, $\mathrm{Cr}$ has the highest second ionisation energy among the given elements.

The correct order for second ionisation energy for the given elements is $\mathrm{Ti}<\mathrm{V}<\mathrm{Mn}<\mathrm{Cr}$.