In the vertical columns of the periodic table, as the atomic numbers increase: the numbers of electron shells increase. the ionization energies increase. the numbers of electrons in the valence shell increase. the tendency to lose electrons decreases. the size of the atom decreases

The numbers of electron shells increase.

Explanation:

The elements in the periodic table are arranged in order of increasing atomic numbers. The horizontal rows are called as periods and vertical columns are called as groups.  

The elements in the groups or vertical columns are arranged in order of increasing atomic numbers and thus contain different number of protons and different number of neutrons. The electrons are added to new energy shells but contain same valence electrons and thus have similar chemical reactivity.

Ionization is defined as the property of an element to lose the valence electron ad ionization energy is the energy required to remove the valence electron. As, the size of an element increases, the valence electrons gets away from the nucleus. So, the attraction between the nucleus and the valence electron decreases, the tendency to lose electrons increases and thus ionization energy decreases.