Answer:
5
Explanation:
Let us look at the values very closely. It is easy to see that the first to the fifth ionization energies of the element are closely related to each other. Recall that the ionization energy increases as the the number of electrons removed from the outermost shell of the atom increases. Hence E1<E2<E3......... The first five ionization energies suggest the removal of valence shell electrons.
However, the sixth and seventh ionization energies shows a jump, the ionization energy suddenly increases by a very high magnitude. This can not suggest the removal of a valence shell electron but the removal of inner or core electrons. Hence the answer.
