Question

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

Options

• d⁴ to d⁵ configuration

• d³ to d⁵ configuration

• d⁵ to d⁴ configuration

• d⁵ to d² configuration

Answer 1

d⁴ to d⁵ configuration

Explanation:

The positive E° value for the couple Mn³⁺/Mn²⁺ is due to the much higher third ionization energy of Mn (where the required change is from half-filled d⁵ (extra stable) to d⁴. As Cr³⁺ (t₂g) is more stable than Cr²⁺, therefore, the E° value for the couple Cr³⁺/Cr²⁺ is negative.