Why is geometrical isomerism not possible in tetrahedral complexes having two different types of unidentate ligands coordinated with the central metal ion?

(N/A) In a tetrahedral complex,all four positions are equivalent with respect to each other.
Because the bond angles between any two ligands are identical $(109.5^{\circ})$,the relative positions of the unidentate ligands remain the same regardless of how they are arranged.
Therefore,no two ligands can be considered 'cis' or 'trans' to each other,making geometrical isomerism impossible in tetrahedral complexes.