Q60 / 200 · NEET 2024 · Chemistry

The $\mathrm{E}^{\circ}$ value for the $\mathrm{Mn}^{3+} / \mathrm{Mn}^{2+}$ couple is more positive than that of $\mathrm{Cr}^{3+} / \mathrm{Cr}^{2+}$ or $\mathrm{Fe}^{3+} / \mathrm{Fe}^{2+}$ due to change of

  • A
    $\mathrm{d}^5$ to $\mathrm{d}^2$ configuration
  • Correct answer
    B
    $\mathrm{d}^4$ to $\mathrm{d}^5$ configuration
  • C
    $d^3$ to $d^5$ configuration
  • D
    $d^5$ to $d^4$ configuration

Solution

$\mathrm{E}_{\mathrm{Mn}^{3+} / \mathrm{Mn}^{2+}}^{\circ}\gt\mathrm{E}_{\mathrm{Cr}^{3+} / \mathrm{Cr}^{2+}}^{\circ} \text { or } \mathrm{E}_{\mathrm{Fe}^{3+} / \mathrm{Fe}^{2+}}^{\circ}$ Electronic configuration of $\mathrm{Mn}^{3+}=[\mathrm{Ar}] 3 d^4$ Electronic configuration of $\mathrm{Mn}^{2+}=[\mathrm{Ar}] 3 d^5$ Electronic configuration of $\mathrm{Cr}^{3+}=[\mathrm{Ar}] 3 d^3$ Electronic configuration of $\mathrm{Cr}^{2+}=[\mathrm{Ar}] 3 d^4$ As $\mathrm{Mn}^{3+}$ from $d^4$ configuration goes to more stable $d^5$ configuration (Half filled), due to more exchange energy in $d^5$ configuration.

Hence, the correct answer is option: 'B'.

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