Which form following elements forms coloured compound in its respective oxidation state?

Step-by-step solution

Transition metal ions form colored compounds when they possess partially filled d-orbitals with unpaired electrons, enabling d-d transitions that absorb visible light. Analyzing the electronic configurations: Sc ³⁺ has configuration [ Ar ] 3d^0 , Zn ²⁺ has [ Ar ] 3d¹⁰ , and Ti ⁴⁺ has [ Ar ] 3d^0 – all lack the necessary unpaired d-electrons for d-d transitions. Cr ³⁺ has configuration [ Ar ] 3d^3 with three unpaired electrons, allowing d-d transitions that produce colored compounds such as the characteristic green