Which of the following ion is expected to be coloured? — Atomic Structure Chemistry Question

💡 Solution & Explanation

Transition metal ions with a partially filled d-subshell (d^1 through d^9 configurations) can absorb specific wavelengths of visible light to promote an electron between split d-orbitals (d-d transitions). This makes their compounds coloured. Let's check the configurations: (a) Zn^2+ (Z = 30): [Ar] 3d^10 (completely filled d-subshell, d-d transition impossible, colourless). (b) Ca^2+ (Z = 20): [Ar] 3d^0 (completely empty d-subshell, colourless). (c) Sn^2+ (Z = 50): Sn is a p-block metal (not transition) with configuration [Kr] 4d^10 5s^2, which lacks any partially filled d-subshell (colourless). (d) V^2+ (Z = 23): [Ar] 3d^3 (partially filled d-subshell, d-d transition possible, coloured). Therefore, only V^2+ is expected to be coloured.