How many geometrical isomers are possible in the following coordination entities?
$(i)$ $[Cr(C_2O_4)_3]^{3-}$
$(ii)$ $[Co(NH_3)_3Cl_3]$

(N/A) $(i)$ For $[Cr(C_2O_4)_3]^{3-},$ no geometrical isomer is possible because the complex contains three identical symmetrical bidentate ligands,which results in a highly symmetric structure.
$(ii)$ For $[Co(NH_3)_3Cl_3],$ two geometrical isomers are possible: the facial $(fac)$ isomer,where the three identical ligands occupy the corners of one triangular face of the octahedron,and the meridional $(mer)$ isomer,where the three identical ligands occupy the positions around the meridian of the octahedron.