Read the passage carefully and answer the Questions.
According to Valence Bond theory, the metal atom or ion under the influence of ligands can use its (n-1)d, ns, np or ns, np, nd orbitals for hybridisation to yield a set of equivalent orbitals of definite geometry such as octahedral, tetrahedral, square planar and so on. These hybridised orbitals are allowed to overlap with ligand orbitals that can donate electron pairs for bonding. While the VB theory, to a larger extent, explains the formation, structures and magnetic behaviour of coordination compounds, it suffers from the many shortcomings. The crystal field theory (CFT) is an electrostatic model which considers the metal-ligand bond to be ionic arising purely from electrostatic interactions between the metal ion and the ligand. The five d orbitals in an isolated gaseous metal atom/ion have same energy, i.e., they are degenerate. This degeneracy is maintained if a spherically symmetrical field of negative charges surrounds the metal atom/ion. However, when this negative field is due to ligands in a complex, it becomes asymmetrical and the degeneracy of the d orbitals is lifted. It results in splitting of the d orbitals. The pattern of splitting depends upon the nature of the crystal field.
Which of the following is not true about the limitations of VBT
Answer & explanation
Correct answer: option 2
The correct answer is Option (2) → It does not explain hybridisation to yield a set of equivalent orbitals
Valence bond theory is built on hybridisation: the metal ion mixes its (n−1)d, ns and np (or ns, np, nd) orbitals into a set of equivalent hybrid orbitals of definite geometry, which then accept electron pairs from the ligands. The passage itself says so in its first sentence.
Option (1) It does not give quantitative interpretation of magnetic data. — A limitation of VB theory. VB theory tells only whether unpaired electrons are present, not the exact magnetic behaviour.
Option (2) It does not explain hybridisation to yield a set of equivalent orbitals — Not a limitation of VB theory. Hybridisation into equivalent orbitals is the very basis of VB theory, so explaining it is what the theory does.
Option (3) It does not explain the colour exhibited by coordination compounds. — A limitation of VB theory. Colour comes from d–d transitions between split d levels, which only crystal field theory describes.
Option (4) It does not give a quantitative interpretation of the thermodynamic or kinetic stabilities of coordination compounds. — A limitation of VB theory. VB theory gives no measure of how stable or how reactive a complex is.
NCERT (2026-27 edition):
Limitations of Valence Bond Theory
