How does the nuclear charge evolve DOWN a Group of the Periodic Table?
The effective nuclear charge DECREASES down a Group of the Periodic Table.
The effective nuclear charge INCREASES across a Period from left to right to right as we face the Table.
Down a Group, however, the valence electrons are further removed from the nuclear core, and a priori we would expect that the effective nuclear charge would decrease. Perhaps the best metric to illustrate is the ionization energy, which certainly decreases down any Group of the Periodic Table.