Let's analyze each of the given options to determine which one is incorrect: Option A: A tetrahedral complex of the type [Ma2b2] does not show geometrical isomerism. A tetrahedral complex [Ma2b2] cannot show geometrical isomerism because the positions of the ligands in a tetrahedral geometry are equivalent. Hence, this statement is correct. Option B: Coordination entities of the type [Ma3b3] do not exhibit geometrical isomerism. Coordination entities of the type [Ma3b3] have a single type of ligand ( a and b ) in a 3:3 ratio, and the distribution of these ligands can lead to different arrangements. These complexes can exhibit geometrical isomerism. Therefore, this statement is incorrect. Option C: Square planar complex of the type [Mabcd] has 3 possible geometrical isomers. In a square planar complex of the type [Mabcd], where M is the metal and a,b,c,d are different ligands, we can indeed have exactly 3 geometrical isomers. Hence, this statement is correct. Option D: In a coordination entity of the type [Ma2(bb)2]2+ only the cis-isomer is optically active. For a coordination entity of the type [Ma2(bb)2]2+, where bb is a bidentate ligand, only the cis-isomer can be optically active as it allows for non-superimposable mirror images. Therefore, this statement is correct. Based on the analysis, the incorrect statement is: Option B Coordination entities of the type [Ma3b3] do not exhibit geometrical isomerism.