Higher second ionisation enthalpies than expected are observed for
Higher second ionisation enthalpies than expected are observed for
Ti, Zn
$\mathrm{Mn}, \mathrm{Fe}$
$\mathrm{V}, \mathrm{Ni}$
$\mathrm{Cr}, \mathrm{Cu}$
Solution
The electronic configuration of $\mathrm{Cr}$ is $[\mathrm{Ar}] 3 d^5 4 s^1$ and that of $\mathrm{Cu}$ is $[\mathrm{Ar}] 3 d^{10} 4 s^1$. Their second ionisation enthalpies are higher than expected because after removal of one electron chromium gets a half-filled electronic configuration and $\mathrm{Cu}$ get a fully-filled $3 d$ electronic configuration. These configuration are more stable than the partial-filled electronic configuration. So, it is very difficult to remove the second electron in both cases.
Thus, option (d) is correct.
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