Final answer:
The exceptionally large increase in ionization energy for chlorine atoms occurs when electrons are removed from the core shell rather than the valence shell, which typically happens after the removal of the seventeenth electron.
Step-by-step explanation:
The question asks for the ionization energy of chlorine atoms that exhibits a particularly high increase over the preceding ionization energy. Ionization energy refers to the energy required to remove an electron from an atom. In the case of chlorine, there is a considerable jump in the energy needed when removing electrons from the core versus the valence electrons. This is attributed to the fact that core electrons are closer to the nucleus and thus experience a stronger electrostatic attraction, making them more difficult to remove.
For chlorine, this large increase typically occurs when electrons are removed beyond the valence shell. When the first valence electron (the seventeenth electron) has been removed, the sixteenth electron resides in a fully filled third shell and is significantly more difficult to remove due to increased electrostatic interactions. Hence, the large increase in ionization energy after the seventeenth electron has been removed indicates the transition from ionizing valence electrons to core electrons.