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.
Select the incorrect statement about the Crystal field splitting in octahedral complexes.
Answer & explanation
Correct answer: option 1
The correct answer is Option (1) → \(d_{x^2-y^2}\) and \(d_{z^2}\) orbitals point towards the axes along the direction of the ligand will experience less repulsion
In an octahedral complex the six ligands lie on the x, y and z axes. A d orbital that points towards the ligands feels more repulsion and rises in energy; one that points between the axes feels less and falls in energy.
Option (1) \(d_{x^2-y^2}\) and \(d_{z^2}\) orbitals point towards the axes along the direction of the ligand will experience less repulsion — Incorrect about octahedral splitting. These two orbitals point straight at the ligands, so they experience more repulsion, not less, and form the higher energy \( e_g \) set.
Option (2) \(d_{xy}, d_{yz}\) and \(d_{xz}\) orbitals are directed between the axes will be lowered in energy — Correct about octahedral splitting. They point between the ligands and are repelled less.
Option (3) the degeneracy of the d orbitals has been removed to yield three orbitals of lower energy, \(t_{2g}\) set — Correct about octahedral splitting. These three orbitals form the lower \( t_{2g} \) set.
Option (4) degeneracy of the d orbitals has been removed to yield two orbitals of higher energy, \(e_g\) set — Correct about octahedral splitting. The gap between the two sets is the crystal field splitting, \( \Delta_o \).
NCERT (2026-27 edition):
Crystal Field Splitting in Octahedral Coordination Entities
