Correct statement(s) about the following coordination species (atomic numbers: Fe 26, Co 27, Ni 28; use the spin-only formula) is(are)

Option A is correct: $\mathrm{Ni^{2+}}$ is $d^8$ and with the weak-field $\mathrm{Cl^-}$ ligand the complex is $sp^3$ tetrahedral with two unpaired electrons, so $\mu=\sqrt{2\times4}=2.83\ \mathrm{BM}$. Option B is correct: cyanide is a strong-field ligand, which pairs the $d^8$ electrons and gives $dsp^2$ square planar geometry with no unpaired electrons. Option C is wrong: $\mathrm{Fe^{3+}}$ is $d^5$, but cyanide is strong field, so the complex is low spin ($t_{2g}^5$) with one unpaired electron and $\mu=1.73\ \mathrm{BM}$. Option D is wrong: $\mathrm{Co^{3+}}$ is $d^6$ and with $\mathrm{NH_3}$ the splitting exceeds the pairing energy, giving $t_{2g}^6$, which is diamagnetic with $d^2sp^3$ hybridisation.