JEE Main · 2022 · 28 Jul 2022 · Shift 1 · d and f Block Elements

The disproportionation of

MnO_{4}^{2 -}

in acidic medium resulted in the formation of two manganese compounds A and B. If the oxidation state of Mn in B is smaller than that of A, then the spin-only magnetic moment (

μ

) value of B in BM is

____

. (Nearest integer)

Answer: 4

Solution

Disproportionation of

MnO_{4}^{2 -}

in acidic medium:

3 MnO_{4}^{2 -} + 4 H^{+} \to 2 MnO_{4}^{-} + MnO_{2} + 2 H_{2} O

Oxidation states:

In $MnO_{4}^{-}$ (A): Mn is +7
In $MnO_{2}$ (B): Mn is +4

Since oxidation state of Mn in B (+4) < A (+7), B is

MnO_{2}

.

For Mn⁴⁺: Electronic configuration is

[A r] 3 d^{3}

(3 unpaired electrons).

Spin-only magnetic moment:

μ = n (n + 2) = 3 (3 + 2) = 15 = 3.873 BM

Nearest integer: 4

JEE Main · 2022 · 28 Jul 2022 · Shift 1 · Integer answer

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