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

JEE Main · 2025 · 02 Apr 2025 · Shift 1 · Coordination Compounds

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 (CN)_{6}]^{4 -}

. The number of electrons present in the

e_{g}

orbital of the complex is ______.

Answer: 1

Solution

Among the four metals the

M X^{3 +} / M X^{2 +}

couple with the highest standard potential belongs to cobalt, so the complex is

[Co (CN) X_{6}] X^{4 -}

with cobalt in the +2 state, a

3 d^{7}

ion. Cyanide is a strong-field ligand, so the octahedral splitting exceeds the pairing energy and the seven d electrons take the low-spin arrangement

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

. The number of electrons in the

e_{g}

orbitals is one.

JEE Main · 2025 · 02 Apr 2025 · Shift 1 · Integer answer

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