Question

why does the atomic radius increase going from top to bottom within a column on the periodic table?
increased number of neutrons
increased number of energy levels
valence electrons
increased number of protons

Explanation:

As you move from top - to - bottom in a group of the periodic table, new energy levels are added. Each new energy level is farther from the nucleus, leading to an increase in the atomic radius. Neutrons do not significantly affect atomic radius. Valence electrons are in the outermost shell and their number remains the same within a group, not causing the radius increase. An increase in protons would attract electrons more strongly and decrease the radius if not for the addition of new energy levels.

Answer:

Increased number of energy levels