The crystal field stabilization energy (CFSE) and magnetic moment (spin-only) of an octahedral aqua complex of metal ion (MZ+) are -0.8Δo and 3.87 BM respectively identify (MZ+).
(2)
H2O (W.F.L) no force pairing hence C.F splitting E = C.F stabilisation energy
Co+2=3d7 t2g5 eg2
C.F.S.E=(-0.4×5+2×0.6)Δ0=-0.8Δ0
μ=3(3+2)=3.87 BM