Predict which of the following will be colourless in aqueous solution ? $Ti^{3+},V^{3+},Sc^{3+},Mn^{2+},Fe^{3+},Co^{2+}$ and $MnO_4^{-}$

Question

$\begin{array}{1 1}(a) \;Co^{2+} , Ti^{3+}\\(b)\;V^{3+} , Mn^{2+} \\(c)\;Sc^{3+}\\(d)\;MnO_4^-\end{array}$