When shielding increases, the attraction between the nucleus and valence electron decreases.
Shielding refers to the phenomenon where inner electrons in an atom partially shield or screen the valence electrons from the full positive charge of the nucleus. As a result, the effective nuclear charge experienced by the valence electrons is reduced.
When the shielding effect increases, more inner electrons are present to shield the valence electrons from the positive charge of the nucleus. This reduces the net positive charge experienced by the valence electrons and weakens the attraction between the nucleus and the valence electron. Therefore, the correct answer to the blank is "decreases."