JEE Main 2025 Apr 3 Shift 2, Chemistry Q10: Colour, Magnetism And Stability Of Co-ordination Compounds

JEE Main2025Apr 3, Shift 2Chemistry

Identify the diamagnetic octahedral complex ions from below ;

A. [Mn(CN) $_{6}$ ] $^{3 -}$

B. [Co(NH $_{3}$ ) $_{6}$ ] $^{3 +}$

C. [Fe(CN) $_{6}$ ] $^{4 -}$

D. [Co(H $_{2}$ O) $_{3}$ F $_{3}$ ]

Choose the correct answer from the options given below :

A
B and D Only
B
A and D Only
C
A and C Only
D
B and C Only

Solution

Use the metal oxidation state, d-electron count, and strength of the ligand field to decide spin state in each octahedral complex.

(A) [Mn(CN) $_{6}$ ] $^{3 -}$ : Mn(III), d $^{4}$ . CN $^{-}$ is strong-field, giving low-spin $t_{2 g}^{4} e_{g}^{0}$ . Four electrons in three $t_{2 g}$ orbitals leave two unpaired. Paramagnetic.

(B) [Co(NH $_{3}$ ) $_{6}$ ] $^{3 +}$ : Co(III), d $^{6}$ . NH $_{3}$ is strong-field for Co(III), giving low-spin $t_{2 g}^{6} e_{g}^{0}$ . All paired. Diamagnetic.

(C) [Fe(CN) $_{6}$ ] $^{4 -}$ : Fe(II), d $^{6}$ . CN $^{-}$ is strong-field, giving low-spin $t_{2 g}^{6} e_{g}^{0}$ . All paired. Diamagnetic.

(D) [Co(H $_{2}$ O) $_{3}$ F $_{3}$ ]: Co(III), d $^{6}$ , but F $^{-}$ and H $_{2}$ O are weak-field. The complex is high-spin $t_{2 g}^{4} e_{g}^{2}$ with four unpaired electrons. Paramagnetic.

$∴$ Only B and C are diamagnetic.

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JEE Main 2025 Apr 3 Shift 2, Chemistry Q10: Colour, Magnetism And Stability Of Co-ordination Compounds

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