The Ionization Energy of an Atom in Its Ground State $\alpha$

Multiple Choice

The ionization energy of an atom in its ground state is:

A) the energy required to remove the least energetic electron
B) the energy required to remove the most energetic electron
C) the energy difference between the most energetic electron and the least energetic electron
D) the same as the energy of a K _$\alpha$ photon
E) the same as the excitation energy of the most energetic electron