In following pairs, the one in which both transition metal ions are colourless is:

Concept: Colour requires partially filled d orbitals ($d^1$–$d^9$). $d^0$ and $d^{10}$ ions are colourless.

| Ion | Config | Colour | |-----|--------|--------| | $\text{Sc}^{3+}$ | $3d^0$ | Colourless ✓ | | $\text{Zn}^{2+}$ | $3d^{10}$ | Colourless ✓ | | $\text{Ti}^{4+}$ | $3d^0$ | Colourless ✓ | | $\text{Cu}^{2+}$ | $3d^9$ | Blue (coloured) ✗ | | $\text{V}^{2+}$ | $3d^3$ | Violet ✗ | | $\text{Ti}^{3+}$ | $3d^1$ | Purple ✗ | | $\text{Mn}^{2+}$ | $3d^5$ | Faint pink ✗ |

Option (1): Both $\text{Sc}^{3+}$ ($d^0$) and $\text{Zn}^{2+}$ ($d^{10}$) are colourless. ✓

Answer: Option (1)