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# Please help! The pair having the same magnetic moment is :[At. No. : Cr=24, Mn=25, Fe=26, Co=27]

The pair having the same magnetic moment is :
[At. No. : Cr=24, Mn=25, Fe=26, Co=27]

• Option 1)

[Cr(H2O)6]2+ and [CoCl4]2−

• Option 2)

[Cr(H2O)6]2+ and [Fe(H2O)6]2+

• Option 3)

[Mn(H2O)6]2+ and [Cr(H2O)6]2+

• Option 4)

[CoCl4]2− and [Fe(H2O)6]2+

Answers (1)
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As we learnt in

Pauli Exclusion Principle -

“No two electrons in an atom can have the same set of four quantum number" .

-

and

Hund’s Rule of Maximum Multiplicity -

"pairing of electrons in the orbitals belonging to the same subshell ( p,d or f ) does not take place until each orbital belonging to that subshell has got one electron each i.e.,It is singly occupied.”

-

magnetic moment $\mu = \sqrt {n \left ( n+2 \right )}$ where n is the number of unpaired electrons.

In given problem $Cr^{2+}$ and $Fe^{2+}$ has same number of unpaired electrons

$Cr^{2+} => 3d^{4}$ four unpaired electrons

$Fe^{2+} => 3d^{6}$ four unpaired electrons

Correct answer is 2

Option 1)

[Cr(H2O)6]2+ and [CoCl4]2−

Incorrect option

Option 2)

[Cr(H2O)6]2+ and [Fe(H2O)6]2+

Correct option

Option 3)

[Mn(H2O)6]2+ and [Cr(H2O)6]2+

Incorrect option

Option 4)

[CoCl4]2− and [Fe(H2O)6]2+

Incorrect option

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