Question

which choice lists two elements with electron configurations that are well - known exceptions to the aufbau principle? * (0.5 points)
cs and cl
fe and co
cr and cu
rb and co
cu and c

Explanation:

The Aufbau principle states that electrons fill lower - energy orbitals before higher - energy ones. Chromium (Cr) and copper (Cu) are well - known exceptions. In Cr, instead of the expected [Ar]4s²3d⁴, it has [Ar]4s¹3d⁵ to achieve a half - filled d - subshell. In Cu, instead of [Ar]4s²3d⁹, it has [Ar]4s¹3d¹⁰ to achieve a fully - filled d - subshell.

Answer:

C. Cr and Cu