The spin-only magnetic moment value of \(\mathrm{M}^{3+}\) ion (in gaseous state) from the pairs \(\mathrm{Cr}^{3+} / \mathrm{Cr}^{2+}\), \(\mathrm{Mn}^{3+} / \mathrm{Mn}^{2}\), \(\mathrm{Fe}^{3+} / \mathrm{Fe}^{2+}\) and \(\mathrm{Co}^{3+} / \mathrm{Co}^{2+}\) that has negative standard electrode potential, is \_\_\_\_ B.M. [Nearest integer]

JEE Main · 2022 · 25 Jul 2022 · Shift 2 · d and f Block Elements

The spin-only magnetic moment value of

M^{3 +}

ion (in gaseous state) from the pairs

Cr^{3 +} / Cr^{2 +}

Mn^{3 +} / Mn^{2}

Fe^{3 +} / Fe^{2 +}

and

Co^{3 +} / Co^{2 +}

that has negative standard electrode potential, is ____ B.M.
[Nearest integer]

Answer: 4

Among the given pairs, only

Cr^{3 +} / Cr^{2 +}

has a negative standard electrode potential:

E_{Cr^{3 +} / Cr^{2 +}}^{0} = - 0.41 V

.

For

Cr^{3 +}

: Electronic configuration is

3 d^{3}

(3 unpaired electrons).

Spin-only magnetic moment:

μ = n (n + 2)

B.M., where

n = 3

μ = 3 (3 + 2) = 15 \approx 3.87

B.M. ≈ 4 B.M. (nearest integer).

JEE Main · 2022 · 25 Jul 2022 · Shift 2 · Integer answer