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 is more positive than that of Cr³⁺/Cr²⁺ or Fe³⁺/Fe²⁺ due to change of

Option 3: d⁴ to d⁵ configuration

Explanation:

Let's analyze the electronic configurations of the ions involved:

Mn³⁺: [Ar] 3d⁴

Mn²⁺: [Ar] 3d⁵

Cr³⁺: [Ar] 3d³

Cr²⁺: [Ar] 3d⁴

Fe³⁺: [Ar] 3d⁵

Fe²⁺: [Ar] 3d⁶

The Mn³⁺/Mn²⁺ couple involves the change from a d⁴ to a d⁵ configuration. The d⁵ configuration is particularly stable due to the half-filled d orbitals. This stability makes the reduction of Mn³⁺ to Mn²⁺ favorable, resulting in a more positive E° value.

In the case of Cr³⁺/Cr²⁺, the change is from d³ to d⁴, and for Fe³⁺/Fe²⁺ it's from d⁵ to d⁶. Neither of these changes leads to the same level of stability as the d⁴ to d⁵ transition.

Therefore, the higher E° value for Mn³⁺/Mn²⁺ is due to the d⁴ to d⁵ configuration change, which results in a stable half-filled d⁵ configuration.