Answer:
Electronegativity is the ability of an atom to attract electrons from another atom. The nucleus of an atom plays a huge role in this ability. Now when you move down a group or a family, the size of the atom increases and the energy level increases as well. This then means that the valence electrons are moving further and further away from nucleus as more energy levels are added. Since the nucleus is moving further, its ability to attract electrons is getting weaker as the distance increases thus, affecting its electronegativity.
