7. The small, but important, energy differences between 3s, 3p, and 3d orbitals are due mainly to
(A) the number of electrons they can hold
(B) their principal quantum number
(C) the Heisenberg uncertainty principle
(D) the penetration effect
(E) Hund's rule

考試觀念本題測驗的是多電子原子中軌域能...