What trend in ionization energy do you see as you go down a group on the periodic table

The first ionization will decrease surely.

First Ionization energy decreases as you move down a group on the periodic table.

First Ionization energy is the energy required to remove the outermost or highest energy electron from the neutral atom in its ground state.

First Ionization energy decreases as you move down a group because electrons are further from the nucleus and thus easier to remove the outermost layer requiring lesser first ionization energy.

On the other hand, as you move across a period, first ionization energy increases because the atomic radius decreases making the atom smaller in size and the outer electrons closer to its nucleus and more strongly attracted to the center; requiring an increase in first ionization energy to remove the outer layer.