The number of species from the following that are involved in sp3d2 hybridization is: [Co(NH3)6]3+, SF6, [CrF6]3-, [CoF6]3-, [Mn(CN)6]3-, and [MnCl6]3-

$sp^3d^2$ hybridization uses outer nd orbitals. These are outer orbital (high-spin) complexes formed with weak field ligands.

$d^2sp^3$ hybridization uses inner (n−1)d orbitals. These are inner orbital (low-spin) complexes formed with strong field ligands.

$Co^{3+}$ electronic configuration: $[Ar]\,3d^6$

$NH_3$ is a strong field ligand. It forces electron pairing in the lower energy $3d$ ($t_{2g}$) orbitals, vacating two inner 3d orbitals available for hybridization.

Sulfur ground state: $[Ne]\,3s^2\,3p^4$. Sulfur has empty 3d orbitals available for bonding expansion.

In $SF_6$, one $3s$ + three $3p$ + two $3d$ orbitals hybridize to form six equivalent $sp^3d^2$ hybrid orbitals, each bonding with a fluorine atom.

$Cr^{3+}$ configuration: $[Ar]\,3d^3$. $F^-$ is a weak field ligand.

Weak field $F^-$ does not cause electron pairing. The three inner $3d$ electrons remain unpaired, so inner $3d$ orbitals cannot be vacated. Hybridization uses outer $4d$ orbitals.

$Co^{3+}$ configuration: $[Ar]\,3d^6$. $F^-$ is a weak field ligand.

Even though $Co^{3+}$ is $d^6$, the weak field $F^-$ does not force electron pairing. Electrons remain in a high-spin arrangement and hybridization involves outer $4d$ orbitals.

$Mn^{3+}$ configuration: $[Ar]\,3d^4$. $CN^-$ is a very strong field ligand.

Strong field $CN^-$ forces maximum pairing. The $3d^4$ electrons pair into two orbitals, vacating two inner $3d$ orbitals that participate in hybridization.

$Mn^{3+}$ configuration: $[Ar]\,3d^4$. $Cl^-$ is a weak field ligand.

Weak field $Cl^-$ cannot force electron pairing. Inner $3d$ orbitals remain occupied, so hybridization uses outer $4d$ orbitals.

Final Summary: