COMEDK 2025 Evening Solved Paper

Concept:Symmetric distribution means each orbital in a set contains exactly one electron (half-filled) or two electrons (fully filled), giving uniform occupancy.Explanation:We determine the d-electron count and spin state for each complex using ligand field strength.• $\left[\mathrm{CoF}_6\right]^{3-}$: $\mathrm{Co}^{3+}$ is $d^6$. $\mathrm{F}^{-}$ is weak-field, so high-spin: $t_{2g}^4 e_g^2$. One $t_{2g}$ orbital has two electrons → not symmetric.• $\left[\mathrm{Mn(CN)_6}\right]^{4-}$: $\mathrm{Mn}^{2+}$ is $d^5$. $\mathrm{CN}^{-}$ is strong-field, so low-spin: $t_{2g}^5 e_g^0$. $t_{2g}$ is uneven (2,2,1) → not symmetric.• $\left[\mathrm{Cr}\left(\mathrm{NH}_3\right)_6\right]^{3+}$: $\mathrm{Cr}^{3+}$ is $d^3$. $\mathrm{NH}_3$ is moderate-field; $d^3$ always gives $t_{2g}^3 e_g^0$. $e_g$ empty → only $t_{2g}$ occupied.• $\left[\mathrm{FeCl}_6\right]^{3-}$: $\mathrm{Fe}^{3+}$ is $d^5$. $\mathrm{Cl}^{-}$ is weak-field, so high-spin: $t_{2g}^3 e_g^2$. Each $t_{2g}$ orbital has one electron and each $e_g$ orbital has one electron → symmetric distribution in both sets.Answer:Option D, $\left[\mathrm{FeCl}_6\right]^{3-}$.