JEE Main 2025 Apr 2 Shift 1, Chemistry Q21: Colour, Magnetism And Stability Of Co-ordination Compounds

JEE Main2025Apr 2, Shift 1Chemistry

A transition metal (M) among Mn, Cr, Co and Fe has the highest standard electrode potential $(M^{3 +} / M^{2 +})$ . It forms a metal complex of the type $[M (C N)_{6}]^{4 -}$ . The number of electrons present in the $e_{g}$ orbital of the complex is ________.

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Solution

Identifying M: Among Mn, Cr, Co and Fe, the standard reduction potential $E^{\circ} (M^{3 +} / M^{2 +})$ is highest for cobalt:

$E^{\circ} (C o^{3 +} / C o^{2 +}) = + 1.82 V$

So $M = C o$ and the complex is $[C o (C N)_{6}]^{4 -}$ with cobalt in the $+ 2$ oxidation state $(d^{7})$ .

Splitting: $C N^{-}$ is a strong-field ligand, so this is a low-spin octahedral complex. The seven $d$ -electrons fill $t_{2 g}$ before $e_{g}$ :

$t_{2 g}^{6} e_{g}^{1}$

Hence the $e_{g}$ set carries 1 electron.

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JEE Main 2025 Apr 2 Shift 1, Chemistry Q21: Colour, Magnetism And Stability Of Co-ordination Compounds

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