Spin-only magnetic moments are to be used where needed. The atomic numbers are Fe=26, Co=27, Ni=28. The correct statement(s) about the following…

A: $\mathrm{Fe^{3+}}$ is $d^5$ and $\mathrm{CN^-}$ is a strong-field ligand, so the configuration is $t_{2g}^5$ with one unpaired electron and $\mu=\sqrt{1(1+2)}=\sqrt3$ BM. Correct. B: $\mathrm{Ni^{2+}}$ is $d^8$; four $\mathrm{Cl^-}$ ligands give a tetrahedral, high-spin complex with two unpaired electrons, $\mu=\sqrt8$ BM. Correct. C: In $[\mathrm{Co(en)_2Cl_2}]^+$ the trans isomer is achiral, while the cis isomer is chiral and exists as a pair of enantiomers, giving $1+2=3$ stereoisomers (checked by enumerating all placements of two cis-spanning chelates and two Cl on an octahedron modulo rotations). Correct. D: $\mathrm{Co^{3+}}$ is $d^6$ and $\mathrm{F^-}$ is a weak-field ligand, so $[\mathrm{CoF_6}]^{3-}$ is high spin $t_{2g}^4e_g^2$ with four unpaired electrons, hence paramagnetic. Incorrect. Answer: A, B, C.