Question

The E° value for the Mn³⁺/Mn²⁺ couple is more positive than that of Cr³⁺/Cr²⁺ or Fe³⁺/Fe²⁺ due to change of

• A. d⁵ to d⁴ configuration
• B. d⁵ to d² configuration
• C. d⁴ to d⁵ configuration
• D. d³ to d⁵ configuration

Answer 1

The Correct Option is C

The E° value for the Mn³⁺/Mn²⁺ couple being more positive than that of Cr³⁺/Cr²⁺ or Fe³⁺/Fe²⁺ can be attributed to electronic configuration changes. This change highlights the special stability associated with the half-filled d-subshell of Mn²⁺. Let's analyze the changes in electronic configurations for these transitions:

Mn³⁺ (d⁴) to Mn²⁺ (d⁵): Manganese goes from a d⁴ to a d⁵ configuration, achieving a half-filled 3d subshell, known for stability due to symmetrical electron distribution.

Cr³⁺ (d³) to Cr²⁺ (d⁴): No special stability is achieved as the d⁴ state is less stable compared to a half-filled or full d-subshell.

Fe³⁺ (d⁵) to Fe²⁺ (d⁶): Iron moves from a half-filled d-subshell to a more than half-filled state, which doesn't provide additional stability.

This analysis demonstrates that the Mn³⁺ to Mn²⁺ transition uniquely benefits from the half-filled d⁵ stability, resulting in a more positive E° value. Therefore, the change in electronic configuration from d⁴ to d⁵ is responsible for the more positive E° value.