Factors contributes to the increase in atomic size within a group in the periodic table as the atomic number increases?

As atomic number increases within a group in the Periodic Table, atomic size increases primarily due to the addition of electron shells. Each successive element has an additional energy level, which places its outermost electrons farther from the nucleus. Although the nuclear charge increases, the effect of increased shielding from inner electrons reduces the effective nuclear charge felt by the outermost electrons, allowing the atomic radius to expand. Consequently, this leads to larger atomic sizes down a group.