The property of elements which increases down a group of the periodic table is

The property that increases down a group in the periodic table is the ionic radius. The ionic radius is the size of an atom, measured from the center of the nucleus to the outermost shell of electrons. As you move down a group in the periodic table, the number of electron shells increases, making the atom larger and the ionic radius larger. This is due to the fact that the outermost electrons are farther away from the nucleus and are not held as tightly as the inner electrons. This results in a larger overall size of the atom.