Question

The first four ionization energy values of an element are $120,240,520,$ and $6420$ kcal. The number of valence electrons in the element is :

Answer 1

As there is very high difference between $I.E{.}_3$ and $I.E{.}_4$ thus it has three electrons in its valence shell. This sudden increase in due to removal of electron from the penultimate orbit.