Manganese has the following electronic configuration $ {}_{25}Mn=1{{s}^{2}},2{{s}^{2}}2{{p}^{6}},3{{s}^{2}}3{{p}^{6}}3{{d}^{5}},4{{s}^{2}} $ It shows +7 oxidation state by losing all the seven electrons in 3d and 4s-sub-shells. Thus, it shows maximum oxidation state. (e.g., in $ KMn{{O}_{4}}, $ O.S. of $ Mn=+7 $ )