Question

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

• A. \(\text{CrO}^{2-}_4\)
• B. \(\text{MnO}^{-}_4\)
• C. \(\text{Cr}_2\text{O}^{2-}_7\)
• D. \(\text{MnO}^{2-}_4\)

Answer 1

The Correct Option is D

To determine which ion exhibits both d-d transition and paramagnetism, we need to assess the electronic configuration and properties of each given ion.

1. \(\text{CrO}^{2-}_4\): Chromium is typically in a +6 oxidation state here, which means it has no d electrons available for d-d transitions. Additionally, ions with a +6 oxidation state are usually diamagnetic due to the absence of unpaired electrons, so it cannot exhibit paramagnetism.
2. \(\text{MnO}^{-}_4\): In this ion, manganese is in a +7 oxidation state, which implies the d-orbitals are empty (no d electrons) which rules out d-d transitions. It is also diamagnetic.
3. \(\text{Cr}_2\text{O}^{2-}_7\): In this ion, chromium is again in a +6 oxidation state. As explained earlier, this does not allow for d-d transitions due to the lack of unpaired d electrons, leading to diamagnetic properties.
4. \(\text{MnO}^{2-}_4\): In this ion, manganese is in a +6 oxidation state. The electronic configuration of manganese is such that the +6 state (Mn^6+) leaves one unpaired electron in the d orbitals. This not only allows for d-d transitions but also enables the ion to be paramagnetic.

Conclusion: The ion \(\text{MnO}^{2-}_4\) exhibits both d-d transition and paramagnetism due to the presence of unpaired d electrons in the manganese ion.