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Match the complexes listed in Group-I with their respective characteristics in Group-II based on the given information. Group-I: (I) [Cr(CN)₆]³⁻ (II) [RuCl₆]²⁻ (III) [Cr(H₂O)₆]²⁺ (IV) [Fe(H₂O)₆]²⁺ Group-II: (P) The t₂g orbitals are occupied by 4 electrons. (Q) The spin-only magnetic moment is 4.9 BM. (R) Forms a low-spin complex. (S) The metal ion has an oxidation state of +4. (T) The complex is a d⁴ species. Given: Chromium (Cr) has an atomic number of 24, Ruthenium (Ru) has an atomic number of 44, and Iron (Fe) has an atomic number of 26. Choose the correct pairing of Group-I with Group-II.

1. I → R, T; II → P, S; III → Q, T; IV → P, Q
2. I → R, S; II → P, T; III → P, Q; IV → Q, T
3. I → Q, S; II → R; III → T; IV → P, T
4. I → Q, T; II → S; III → P, T; IV → Q, R

Correct answer: I → R, T; II → P, S; III → Q, T; IV → P, Q

Solution

The pairing is based on the electronic configuration and ligand field effects of each complex. [Cr(CN)₆]³⁻ is a low-spin d³ complex due to strong field CN⁻ ligands, matching R and T. [RuCl₆]²⁻ has a +4 oxidation state and a d⁴ configuration, matching P and S. [Cr(H₂O)₆]²⁺ has a high-spin d⁴ configuration, matching Q and T. [Fe(H₂O)₆]²⁺ is a high-spin d⁶ complex with 4.9 BM magnetic moment, matching P and Q.

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