Which of the following is a limitation of Werner's co-ordination theory?

Magnetic properties of the complexes can be predicted easily.

The correct answer is option 4. Magnetic properties of the complexes can be predicted easily.

The limitation of Werner's coordination theory among the options provided is magnetic properties of the complexes can be predicted easily.

Werner's coordination theory, proposed by Alfred Werner in the early 20th century, was revolutionary in understanding the structure and bonding in coordination compounds. However, it does have its limitations, and one of them is related to predicting the magnetic properties of coordination complexes.

Magnetic Properties:  

Werner's coordination theory primarily focuses on the geometric arrangement and bonding between metal ions and ligands. It does not provide a straightforward method to predict the magnetic properties of coordination complexes.

Magnetic properties such as whether a complex is paramagnetic or diamagnetic depend on factors like the number of unpaired electrons in the metal's d-orbitals, which are influenced by crystal field theory and ligand field theory rather than Werner's coordination theory.

Crystal field theory, developed later, provides a framework to understand how ligands affect the splitting of d-orbitals and consequently the magnetic behavior of metal ions in complexes.

Other Options Explained:

Each metal ion possesses two types of valency: This statement aligns with Werner's coordination theory, which proposed primary valencies (satisfied by anions or ligands) and secondary valencies (satisfied by neutral molecules or ions).

Primary valencies are satisfied by anions only: This statement is not entirely accurate according to Werner's theory, as primary valencies can be satisfied by both anions (like halides) and neutral molecules (like water).

Secondary valencies are satisfied by the ions or the neutral electron-pair donor molecules: This statement is consistent with Werner's coordination theory, which introduced the concept of secondary valencies being satisfied by neutral ligands or ions.

Conclusion: Among the given options, the limitation of Werner's coordination theory is that it does not provide an easy method to predict the magnetic properties of coordination complexes. Magnetic properties are better understood through crystal field theory, which builds upon Werner's insights into coordination chemistry.