Match the following:
The correct answer is

$\mathrm{V}^{4+}, \mathrm{Ti}^{3+}$ and $\mathrm{Ni}^{2+}$ having unpaired electrons in $d$-subshell. Therefore, there ions show $d$ - $d$ transition and form different colours. $\mathrm{Ti}^{4+}$ does not have unpaired electrons therefore, it is colourless. \begin{array}{llll} \hline & lons & & \multicolumn{1}{c}{\begin{array}{c} Colour \\ (\mathrm{d}-\mathrm{d} transition ) \end{array}} \\ \hline (A) & \mathrm{V}^{4+} & (\mathrm{IV}) & Blue colour \\ \hline (B) & \mathrm{Ti}^{3+} & (\mathrm{II}) & Purple \\ \hline (C) & \mathrm{Ti}^{4+} & (I) & Colourless \\ \hline (D) & \mathrm{Ni}^{2+} & (III) & Green \\ \hline \end{array} Thus, option (1) is correct.