In an octahedral structure, the pair of $$d$$ orbitals involved in d²sp³ hybridisation is

CN^$$-$$ is a strong field ligand. This is due to the fact that

Among [Ni(CO)₄], [Ni(CN)₄]^2$$-$$, [NiCl₄]^2$$-$$ species, the hybridisation states at the Ni atom are, respectively
[Atomic number of Ni = 28]

The number of unpaired electrons in the complex ion [CoF₆]^3$$-$$ is
(Atomic no. : Co = 27)