When ${\mathrm{MnO}}_2$ is fused with KOH in air, it gives

When ${\mathrm{MnO}}_2$ is fused with KOH in the presence of air, the result is the green potassium manganate ${\mathrm{K}}_2{\mathrm{MnO}}_4$.

$2{\mathrm{MnO}}_2+4\mathrm{KOH}+{\mathrm{O}}_2\to 2{ \mathrm{K}}_2{\mathrm{MnO}}_4+2{\mathrm{H}}_2\mathrm{O}$