Chemistry - Complete d-block Question with Solution | TestHub

$\begin{array}{rl}{\mathrm{Cu}}^{2+}[\mathrm{Ar}]3{\mathrm{d}}^9,& {\mathrm{Ti}}^{4+}[\mathrm{Ar}]3{\mathrm{d}}^0\\ & {\mathrm{Co}}^{2+}[\mathrm{Ar}]3{\mathrm{d}}^7,{\mathrm{Fe}}^{2+}[\mathrm{Ar}]3{\mathrm{d}}^6\end{array}$ $1,3,4$ are coloured ions hence the answer is $b$.