Which of the following sets of aqueous ions is entirely colourless?

Question

Professor PC Thomas Classes · Answer

Colour in transition metal ions arises from d-d transitions. $	ext{Sc}^{3+}$ ($3d^0$), $	ext{Ti}^{4+}$ ($3d^0$), and $	ext{Cu}^+$ ($3d^{10}$) have either empty or completely filled d-orbitals, making d-d transitions impossible and the ions colourless.