Which of the following is a limitation of Werner's coordination theory?
Answer & explanation
Correct answer: option 4
The correct answer is Option (4) → Magnetic properties of the complexes cannot be predicted easily
Werner’s theory explained the formulas and structures of complexes with two kinds of valence, primary and secondary.
It could not explain why complexes have characteristic magnetic and optical properties; later theories such as valence bond theory and crystal field theory were needed for this. Not being able to predict the magnetic properties is therefore a limitation of the theory.
Why the other options are incorrect
Option (1) Each metal ion possesses two types of valency — Incorrect. This is the first postulate of the theory (primary and secondary valences), not a limitation.
Option (2) Primary valencies are satisfied by anions only — Incorrect. This is a postulate: primary valences are ionisable and are satisfied by negative ions, such as the three \( \ce{Cl^-} \) ions in \( \ce{[Co(NH3)6]Cl3} \).
Option (3) Secondary valencies are satisfied by the ions or the neutral electron-pair donor molecules — Incorrect. This is also a postulate: secondary valences are non-ionisable, are satisfied by neutral molecules or negative ions, and equal the coordination number.
NCERT (2026-27 edition):
5.5 Bonding in Coordination Compounds – “Werner was the first to describe the bonding features in coordination compounds. But his theory could not answer basic questions like:
…
(iii) Why coordination compounds have characteristic magnetic and optical properties?
Many approaches have been put forth to explain the nature of bonding in coordination compounds viz. Valence Bond Theory (VBT), Crystal Field Theory (CFT), Ligand Field Theory (LFT) and Molecular Orbital Theory (MOT).”