Question

which choice lists two elements with ground-state electron configurations that are well known exceptions to the Aufbau principle?
a) Cu and C
b) Cr and Cu
C) Cs and Cl
D) Rb and Co
E) Fe and Co

i think it's B right?

Answer 1

Yes. The elements before the half-filled and filled d shells are notorious exceptions to the Madelung rules. Note that they are NOT exceptions to the Aufbau principle (this question is badly worded), because the electrons still go into the lowest-energy orbital. It's just that the lowest energy orbital is no longer the one predicted by the Madelung rules (also called the n+l rules and some other names).