Question

In which of the given diagrams is Aufbau rule and Hund's rule both violated?

• A.
• B.
• C.
• D.

Answer 1

The correct option is C

The aufbau principle says that electrons fill the lower energy orbitals before going to higher energy ones. Hund's rule says pairing of electrons can occur only if the available degenerate orbitals are first half filled. Also, the half filled orbitals must have the same spin, when pairing happens, the spin is opposite to the existing electrons that are present in the half - filled orbitals.
If there are 4 electrons, two would go to ns (Aufbau) and two - same spin electrons in np (Hund's).
If there are 5 electrons, there would be two in ns (Aufbau) and three half - filled in np (Hund's).
If there are 6 electrons, there would be two in ns (Aufbau) and 4 in np where the first subshell has two paired electrons, and the other two p sub shells would have one unpaired electron each of the same spin(Hund's).
In the given options, the first option violate Aufbau, the second is the correct representation, the third violates both Aufbau and Hund's. The last option violates Hund's rule as pairing is shown without all orbitals being half-filled.
The third option is the answer as it violates both of them.