In the preparation of ${\mathrm{KMnO}}_4$, pyrolusite (${\mathrm{MnO}}_2$) is first converted to potassium manganate (${\mathrm{K}}_2{\mathrm{MnO}}_4$). In this conversion, the oxidation state of manganese changes from

The oxidation state of Mn in ${\mathrm{MnO}}_2$ ₌ +4

The Oxidation state of Mn in ${\mathrm{K}}_2{\mathrm{MnO}}_4$= +6

The oxidation state of manganese changes from +4 to +6 in the conversion.

Hence, the correct answer is option (D) +4 to +6.