Correct option is D
The Laporte rule is a rule that explains the intensities of absorption spectra for chemical species. It is a selection rule that rigorously applies to atoms, and to molecules that are centrosymmetric, i.e. with an inversion centre. It states that electronic transitions that conserve parity are forbidden. Thus, transitions between two states that are each symmetric with respect to an inversion centre will not be observed. Transitions between states that are antisymmetric with respect to inversion are forbidden as well. In the language of symmetry, g (gerade = even (German)) → g and u (ungerade = odd) → u transitions are forbidden. Allowed transitions must involve a change in parity, either g → u or u → g.
For atoms s and d orbitals are gerade, and p and f orbitals are ungerade. The Laporte rule implies that s to s, p to p, d to d, etc. transitions should not be observed in atoms or centrosymmetric molecules. Practically speaking, only d-d transitions occur in the visible region of the spectrum. The Laporte rule is most commonly discussed in the context of the electronic spectroscopy of transition metal complexes.
During electronic transition if spin of the electron is not changed, then the transition is spin allowed. This is because an electromagnetic radiation usually cannot change the relative orientation of an electron spin.
