Statement I: Coordination isomerism occurs when both cation and anion are complex ions

Statement II: The complex with coordination number 6 form octahedral complexes involving either sp³d² or d²sp³ hybridization

Both Statement I and statement II are true but statement II is not the correct explanation for statement I

The correct answer is option 2. Both Statement I and statement II are true but statement II is not the correct explanation for statement I.

Statement I: Coordination isomerism occurs when both cation and anion are complex ions.

Statement I is true.  Coordination isomerism occurs when there is an exchange of ligands between the cationic and anionic parts of a coordination compound. In such cases, both the cation and anion are complex ions. For example, consider the coordination isomers of the complex \([Co(NH_3)_6][Cr(CN)_6]\). In one isomer, the cobalt ion is surrounded by six ammonia ligands, and the chromium ion is surrounded by six cyanide ligands. In the other isomer, the cobalt ion is surrounded by six cyanide ligands, and the chromium ion is surrounded by six ammonia ligands.

Statement II: The complex with coordination number 6 forms octahedral complexes involving either sp³d² or d²sp³ hybridization.

Statement II is also true. Complexes with coordination number 6 often form octahedral complexes. The coordination number 6 indicates that there are six ligands surrounding the central metal ion. In octahedral complexes, the metal ion utilizes either sp³d² hybridization or d²sp³ hybridization to form six sigma (σ) bonds with the six ligands. These hybridization schemes involve the mixing of the d and s orbitals to form a set of six equivalent hybrid orbitals, which are then used for bonding with the ligands.

However, Statement II is not the correct explanation for why coordination isomerism occurs when both cation and anion are complex ions (Statement I). Coordination isomerism is not related to the hybridization of the central metal ion but rather to the exchange of ligands between the cationic and anionic parts of the coordination compound.

Therefore, the correct answer is Option 2: Both Statement I and Statement II are true, but Statement II is not the correct explanation for Statement I.