# Is the Aufbau principle violated in the diagram (b)?

In which of the following diagrams is the Aufbau principle violated?

Ignoring the Hund principle, the Aufbau principle states that electrons have to first fill the lowest energy levels. Now the energy level of the s-orbital has to be the lowest, and only in the option (b) the s-orbital is not filled fully. So the answer is (b).

Is my reasoning correct?

• Well, yes, you're right. :) According to the Aufbau principle orbitals with a lower $n + l$ value are filled before those with higher $n + l$ values, so $n \mathrm{s}$ should be filled before $n \mathrm{p}$. – Wildcat Jul 6 '15 at 16:54
• The image in this question is now broken, and therefore the question is completely unclear. This is why people need to write the question out in full, not rely on external sources or displays. – Nij Jun 5 '17 at 19:41
• Had it been on the violation of Hund's rule then option (c) would be the answer. As it first fills singly when all the orbitals are singly occupied only then pairing of electrons commence. what do you say. – Amtul Ahad Jun 25 '19 at 7:20