KCET 2025 Chemistry Paper

In transition metal ions, the coloration typically depends on the presence of unpaired electrons in the d-orbitals. lons with either completely empty d-orbitals ( d0 ) or fully filled d-orbitals ( d10 ) do not exhibit d-d transitions, which are responsible for colored compounds. As a result, these ions tend to be colorless.
The Sc3+ ion has the electron configuration [Ar]3d0, meaning its d-orbitals are empty.
The Zn2+ ion has the electron configuration [Ar]3d10, indicating fully filled d-orbitals.
Since both Sc3+ and Zn2+ lack the d-d electron transitions necessary for color, they are colorless.