The incorrect statement among the given options is Option A. Explanation: Option A: The statement claims that a square planar complex of type Mabcd, where each of a,b, c, d are unidentate ligands, can exhibit geometric isomerism including one cis-form and two trans-forms. However, this is incorrect. In a square planar complex with four different ligands, there cannot be two different trans-forms, because the term 'trans' describes ligands that are directly opposite each other. With four different ligands, there is only one arrangement that can be considered trans (with any two specific ligands opposite each other). Therefore, a square planar complex Mabcd can indeed have a cis-form but only one possible trans-form. This error makes Option A incorrect. To clarify using positional notation, if we assign the ligands as follows in a square plane: a at position 1 b at position 2 c at position 3 d at position 4 A trans-configuration, for instance, could be where ' a ' is trans to ' c ' and ' b ' is trans to ' d '. Any other arrangement merely reshuffles these positions but doesn't offer a fundamentally different 'trans' scenario, where a direct geometric opposition of ligands changes. Option B: This is correct. [ [Co(NH3)5‌NO2]Cl2 does exist in two forms - one where NO2 acts as a ligand through nitrogen (nitro) and another through oxygen (nitrito). These forms are indeed linkage isomers, displaying different properties and colors. Option C: The statement is correct. [Fe(CN)6]3− is a low spin complex. Cyanide is a strong field ligand causing the electrons in iron to pair up into the lower energy orbitals (d-orbitals), resulting in a low spin state. Option D: This statement is accurate. cis- and trans- [CrCl2(ox)2]3− differ in the spatial arrangement of the chloride ligands. The trans-isomer, where the chloride ligands are placed opposite each other, will be optically inactive because it has a mirror plane dividing it into two symmetrical halves, thus showing no optical activity.