JEE Main 2025 Apr 7 Shift 2, Chemistry Q15: Colour, Magnetism And Stability Of Co-ordination Compounds

JEE Main2025Apr 7, Shift 2Chemistry

The number of unpaired electrons responsible for the paramagnetic nature of the following complex species are respectively :

[Fe(CN) $_{6}$ ] $^{3 -}$ , [FeF $_{6}$ ] $^{3 -}$ , [CoF $_{6}$ ] $^{3 -}$ , [Mn(CN) $_{6}$ ] $^{3 -}$

A
1, 5, 4, 2
B
1, 5, 5, 2
C
1, 1, 4, 2
D
1, 4, 4, 2

Solution

CN $^{-}$ is a strong field ligand that causes pairing of electrons in the $t_{2 g}$ set, while F $^{-}$ is a weak field ligand that leaves electrons unpaired as far as possible.

[Fe(CN) $_{6}$ ] $^{3 -}$ : Fe $^{3 +}$ is $d^{5}$ ; strong field CN $^{-}$ gives $t_{2 g}^{5} e_{g}^{0}$ , leaving 1 unpaired electron.

[FeF $_{6}$ ] $^{3 -}$ : Fe $^{3 +}$ is $d^{5}$ ; weak field F $^{-}$ gives high-spin $t_{2 g}^{3} e_{g}^{2}$ , leaving all 5 electrons unpaired.

[CoF $_{6}$ ] $^{3 -}$ : Co $^{3 +}$ is $d^{6}$ ; weak field F $^{-}$ gives high-spin $t_{2 g}^{4} e_{g}^{2}$ , leaving 4 unpaired electrons.

[Mn(CN) $_{6}$ ] $^{3 -}$ : Mn $^{3 +}$ is $d^{4}$ ; strong field CN $^{-}$ gives low-spin $t_{2 g}^{4} e_{g}^{0}$ , leaving 2 unpaired electrons.

$∴$ The unpaired electron counts are 1, 5, 4, 2 respectively.

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JEE Main 2025 Apr 7 Shift 2, Chemistry Q15: Colour, Magnetism And Stability Of Co-ordination Compounds

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