Final answer:
Mg₃[Cr(CN)₆]₂ would be paramagnetic due to unpaired electrons in the d orbitals of Cr³⁺.
Step-by-step explanation:
Would you expect Mg₃[Cr(CN)₆]₂ to be diamagnetic or paramagnetic? The answer is it would be paramagnetic, based on the electron configuration of the chromium ion present in the compound. To understand why we should look at the oxidation state and electron configuration of chromium (Cr) within the complex.
Chromium generally has an electron configuration of [Ar] 3d⁵ 4s¹. However, when chromium is in the +3 oxidation state, as it would be in the named complex (since the cyanide ions are each -1, and there are 6 of them, the total charge is -6 which is balanced by three +2 magnesium ions), its electron configuration becomes [Ar] 3d³.
These 3 electrons in the d-orbitals are unpaired, making the substance paramagnetic. So, the correct choice is d) Paramagnetic; Unpaired electrons in the d orbitals of Cr³⁺.