Which of the Following Provides the Best Evidence for the Presence

Multiple Choice

Which of the following provides the best evidence for the presence of the electron shell structure of atoms?

A) The decrease in ionization energy going down a group.
B) The increase in ionization energy across a period.
C) That the value of m_s can be +1/2 or -1/2
D) That the ionization energy of O is less than the ionization energy of N.
E) All of the above provide evidence for the shell structure of atoms.