Answer:
Going down a family means the elements are getting larger. As more electrons surround the positively charged nucleus, they reduce the attractive electrostatic force because they are further away, and existing electrons repulse them.
Step-by-step explanation:
Electronegativity is a measure of the attraction an element has for electrons. Fluorine has a high electronegativity (2.98), while Francium does not (0.7). Fluorine more readily attracts other electrons. When going down a family on the periodic table, electronegativity decreases. This is because the existing electrons have already filled the electron shells closest to the positive nucleus. A new electron arriving near Francium doesn't experience the full attraction of the nucleus since it so far away. The existing electrons form a repulsive barrier.