JEE Main 2025 Jan 23 Shift 1, Chemistry Q10: Colour, Magnetism And Stability Of Co-ordination Compounds

JEE Main2025Jan 23, Shift 1Chemistry

The d-electronic configuration of an octahedral Co(II) complex having magnetic moment of 3.95 BM is :

A
$t_{2 g}^{6} e_{g}^{1}$
B
$t_{2 g}^{3} e_{g}^{0}$
C
$t_{2 g}^{5} e_{g}^{2}$
D
$e^{4} t_{2}^{3}$

Solution

Co(II) has the electronic configuration $[A r] 3 d^{7}$ , so there are 7 d-electrons to place.

From $μ = n (n + 2)$ , $μ = 3.95$ BM gives $n (n + 2) \approx 15.6$ , so $n \approx 3$ unpaired electrons.

In an octahedral field with 7 electrons, the high-spin arrangement gives $t_{2 g}^{5} e_{g}^{2}$ which contains exactly 3 unpaired electrons (two paired pairs in $t_{2 g}$ , one unpaired in $t_{2 g}$ , and two unpaired in $e_{g}$ ).

$∴$ Configuration is $t_{2 g}^{5} e_{g}^{2}$ .

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JEE Main 2025 Jan 23 Shift 1, Chemistry Q10: Colour, Magnetism And Stability Of Co-ordination Compounds

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