Question

The correct statement among are:
a)Valence bond theory cannot explain the colour exhibited by the transition metal complexes.
b)Valence bond theory can predict quantitatively the magnetic properties of transition metal complexes.
c)Valence bond theory cannot distinguish ligands as weak and strong field ones.
A.a and b only
B.a, b and c
C.a and c only
D.b and c only

Answer 1

Hint: The strong and weak field ligand was distinguished by CFT that is crystal field theory. They give us the cause and effect of d-d transitions. The magnetic properties can be determined from the structure which is given by VBT.

Complete step by step solution:
Colour of complexes depends upon the electronic transitions that are made by the electron in the d orbital, but the valence bond theory does not give any clear explanation of the colour exhibited by the complexes. Instead the CFT clearly gives account for the colour shown by complexes by showing the d-d transition. So statement one is correct.
The magnetic properties of transition metals can be predicted by the number of unpaired electrons present by Filling of electron in an orbital and hence can predict the magnetic property whether diamagnetic or paramagnetic. The VBT does not give quantitative behavior it only provides us qualitative nature.
The strong field and weak field ligand was determined using the spectrochemical series that was prepared experimentally and VBT does not discuss any such series.
So ‘a’ and ‘c’ are correct statements and ‘b’ is incorrect.

Hence the correct option is C

Note: VBT valence bond theory assumes that the bond formed between metal and ligand is polar covalent bond. Ligand is a species which tends to donate electrons to the metal and the metal has D orbitals in which the metals accept electrons, hence a polar covalent bond is formed. Since Werner theory failed to explain the directional properties of ligands and valence bond theory was quite successful in explaining the structure and the bond linking in the coordination complexes.