Which of the following statement(s) is/are the drawbacks of valence bond theory?

Both Option 1 and Option 2 are correct

The correct answer is option 4. Both Option 1 and Option 2 are correct.

Valence bond theory is a model that describes the bonding in coordination complexes by assuming that the metal ion forms covalent bonds with the ligands. However, the valence bond theory has some drawbacks.

It cannot determine the thermodynamic stability of complexes. Valence bond theory only considers the energetics of the individual bonds between the metal ion and the ligands. It does not consider the overall stability of the complex, which is determined by the interplay of the individual bond energies and the entropy of the complex.

It cannot determine the spectral properties of complexes. The spectral properties of complexes are determined by the electronic transitions that can occur between the different energy levels of the complex. Valence bond theory does not provide a good description of these energy levels, so it cannot be used to predict the spectral properties of complexes.

Valence bond theory is valid only for a few complexes of Co and Cr. Valence bond theory is based on the assumption that the metal ion forms covalent bonds with the ligands. However, this assumption is not always valid. For example, in some complexes, the metal ion may form dative bonds with the ligands. Valence bond theory does not provide a good description of these dative bonds, so it is not always accurate for these complexes.

Therefore, the drawbacks of valence bond theory include the fact that it cannot determine the thermodynamic stability of complexes, it cannot determine the spectral properties of complexes, and it is only valid for a few complexes of Co and Cr.