the magnetic moment of cobalt in hg[co(scn4)]
In Hg[Co(SCN)4] complex, Cobalt is present as Co+2 which has 3d7, it means it has 3 unpaired electrons.
Magnetic moment μ = 
where, n = number of unpaired electrons
n = 3 for Co+2
μ = 
= 
= 3.99 B.M.