[Co(CN)6]4− x+6×(−1)=−4 x=+2 Co2+:[Ar]3d7 and CN−is a strong field ligand which can pair electron of central atom.
It has one unpaired electron (n) in 4 d-subshell. So spin only magnetic moment (µ)=√n(n+2) B.M where n= number of unpaired electrons. µ=√3 B.M µ=1.73BM