The electronic configuration or given ions are: $ T{{i}^{3+}}(19)=1{{s}^{2}},2{{s}^{2}}2{{p}^{6}},3{{s}^{2}}3{{p}^{6}}3{{d}^{1}} $ $ S{{c}^{3+}}(18)=[Ar] $ $ M{{n}^{2+}}(23)=[Ar]\,3{{d}^{5}} $ $ Z{{n}^{2+}}(28)=[Ar]\,3{{d}^{10}} $ As, $ M{{n}^{2+}} $ has maximum number of unpaired electrons (5), hence, it shows maximum magnetic moment.