Electronic configuration of Mn is (Z=25)=[Ar]3d54s2∴ Electronic configuration of Mn4+ is Mn4+=[Ar]3d3 Thus, Mn4+ has 3 -unpaired electron and its spin only magnetic moment (μ) is, μ=n(n+2)BM where, n= number of unpaired electrons. μ=3(3+2)⋅BM⇒μ=15=3.87BM≈4BM