In which of the following compound manganese shows maximum radius?

Oxidation state of manganese in ${\mathrm{MnO}}_2$ is $+4,$in ${\mathrm{KMnO}}_4$ is +7, in $\mathrm{MnO}$​ is +2 and in ${\mathrm{K}}_3\left[\mathrm{Mn}(\mathrm{CN}{)}_6\right]$ is +3. Radius reduces when oxidation state rises because fewer electrons are available and nucleas must now draw fewer electrons. Therefore, the compound with the biggest radius has manganese in the lowest oxidation state.
Manganese therefore displays its greatest radius in$\mathrm{MnO}$.