Class 12 NEET Chemistry Coordination Compounds

Concept:Spin-only magnetic moment depends on the number of unpaired electrons. Strong-field ligands cause pairing, reducing unpaired electrons.Explanation:For each complex, find the metal ion's oxidation state and d-configuration. Then decide the number of unpaired electrons based on ligand field strength.A. $\left[\mathrm{Ti}\left(\mathrm{H}_2 \mathrm{O}\right)_6\right]^{3+}$: Ti is +3, electron config $[\mathrm{Ar}]3d^1$. $\mathrm{H}_2\mathrm{O}$ is weak field. Unpaired electrons = 1.B. $\left[\mathrm{Mn}(\mathrm{CN})_6\right]^{3-}$: Mn is +3, $[\mathrm{Ar}]3d^4$. $\mathrm{CN}^-$ is strong field, pairing occurs: $t_{2g}^4 e_g^0$. Unpaired electrons = 2.C. $\left[\mathrm{Fe}(\mathrm{CN})_6\right]^{3-}$: Fe is +3, $[\mathrm{Ar}]3d^5$. Strong field: $t_{2g}^5 e_g^0$. Unpaired electrons = 1.D. $\left[\mathrm{Co}\left(\mathrm{NH}_3\right)_6\right]^{3+}$: Co is +3, $[\mathrm{Ar}]3d^6$. $\mathrm{NH}_3$ is strong field for Co(III): $t_{2g}^6 e_g^0$. Unpaired electrons = 0.The highest number of unpaired electrons is 2 (option B), giving the largest spin‑only magnetic moment.Answer:B. $\left[\mathrm{Mn}(\mathrm{CN})_6\right]^{3-}$