The ionization energy of a certain atom is 5.12eV above the ground state. The atom can also emit a 3.40eV photon when it transitions from an excited state X to the ground state. If an atom is first prepared in state X, what minimum photon energy is required to ionize it?
a) 5.12eV
b) 3.40eV
c) 1.72eV
d) 8.52eV