Question

Which one of the following ions exhibits d-d transition and paramagnetism as well?

Options

• \[\ce{MnO^-_4}\]

• \[\ce{Cr2O^{2-}_7}\]

• \[\ce{CrO^{2-}_4}\]

• \[\ce{MnO^{2-}_4}\]

Answer 1

\[\ce{\mathbf{MnO^{2-}_4}}\]

Explanation:

The d-d transitions occur in ions that have partially filled d-orbitals. Paramagnetism is shown by species that contain unpaired electrons. The metal ions are in +6 or +7 oxidation states, which means no unpaired d-electrons, so they are diamagnetic and do not show d-d transitions. But in \[\ce{MnO^{2-}_4}\], Manganese is in +6 oxidation state. Its electron configuration is [Ar] 3d¹, so it has one unpaired electron. Therefore, it is paramagnetic and can show a d-d transition.