Which of the following coordination compounds cannot show geometrical isomerism?

[Co(en)₃]³⁺

The correct answer is option 2. [Co(en)₃]³⁺

Geometrical isomerism is indeed common in square planar and octahedral complexes, as you have correctly mentioned.

Square planar complexes with the general formula \([MA_2X_2]^{±n}\), \([MA_2XY]^{±n}\), \([MABX_2]^{±n}\), \([MABXY]^{±n}\), \([M(AB)_2]^{±n}\) can show geometrical isomerism due to the presence of different ligands (X and Y) in cis and trans positions relative to each other.

Octahedral complexes with the general formula \([MA_4X_2]\), \([MA_4XY]\), and \([M(AA)_2X_2]\) also show geometrical isomerism. In these cases, geometrical isomerism arises from the different spatial arrangements of ligands around the central metal ion.

Therefore, the correct answer to the original question is that all the given coordination compounds can show geometrical isomerism.