Why is the electron configuration for copper 1 s 2 2 s 2 2 p 6 3 s 2 3 p 6 3 d 10 4 s 1 instead
of 1 s 2 2 s 2 2 p 6 3 s 2 3 p 6 3 d 9 4 s 2 ?
A The 4 s orbital has higher energy than the 3 d orbital.
B Electrons occupy orbitals of the highest energy levels first.
C A filled sublevel is more stable than a half-filled sublevel.