[Mn+2(CN)6]−4 Mn+2→3d54s04p CN−is strong ligands so creates back paring effect of (n−1) d orbitals configuration
So, unpaired e−=1 µ=√n(n+2) B.M µ=1.73 B.M And in [MnBr4]−2 Br is a weak ligands so no back pairing effect on (n−1) d orbital so, unpaired e−is =5 µ=√5(5+2)=√35=5.92 B.M