Generally, when going down a group on the periodic table:

atomic radii decrease

ionic radii increase

electronegativity increases

reactivity decreases

The correct answer is ionic radii increase.

The ionic radii decrease as one move across the periodic table, that is, from left to right, while the ionic radius increases as one move from top to bottom on the periodic table. As one moves down a group in the periodic table, the supplementary layers of electrons are being added that usually results in the increase of the ionic radius as one moves down the periodic table.