Match the complex ions in List-I with their properties in List-II. Fe=26, Co=27, Ni=28.) List-I: (P) [Fe(CN)6]^3-; (Q) [CoF6]^3-; (R) [Ni(CN)4]^2-…

(P) $\mathrm{Fe^{3+}}$ is $d^5$; $\mathrm{CN^-}$ is a strong-field ligand, so the configuration is low spin $t_{2g}^5$ with one unpaired electron: $\mu=\sqrt{3}=1.73\ \mathrm{BM}$ $\Rightarrow$ 1.
(Q) $\mathrm{Co^{3+}}$ is $d^6$; $\mathrm{F^-}$ is a weak-field ligand, so the complex is high spin $t_{2g}^4e_g^2$ with four unpaired electrons $\Rightarrow$ 3.
(R) $\mathrm{Ni^{2+}}$ is $d^8$; with the strong-field $\mathrm{CN^-}$ it forms a square planar $dsp^2$ complex with all electrons paired, hence diamagnetic $\Rightarrow$ 2.
(S) With the weak-field $\mathrm{Cl^-}$, $\mathrm{Ni^{2+}}$ ($d^8$) forms a tetrahedral $sp^3$ complex with two unpaired electrons: $\mu=\sqrt{8}=2.83\ \mathrm{BM}$ $\Rightarrow$ 4.
No complex in List-I has $t_{2g}^3e_g^0$, so (5) is a distractor. Correct code: P→1, Q→3, R→2, S→4.