In ${\left[{\mathrm{CoF}}_6\right]}^{3-},{\mathrm{Co}}^{3+}$ uses outer d orbits (4d) in sp³d² hybridization. The number of unpaired electrons present in complex ion is

As the Co³⁺ has a configuration as follows: [Ar]3d⁶4s⁰ ,
Now, as the F⁻ is the weak field ligand, so does not cause the paring of the 3d⁶ electrons, so it has 2 pair electrons and 4 unpaired electrons in 3d orbitals.
In [CoF_6​]³⁻,Co³⁺ uses outer d orbitals (4d) in sp³d² hybridization. The number of unpaired electrons present in complex ion is 4.