What makes isoelectronic biggest or smallest?

Answer 1

Isoelectronic species are atoms or ions that have the same number of electrons, resulting in similar electronic configurations. The size of these species can vary based on their nuclear charge; species with a higher positive charge (more protons) will attract electrons more strongly, resulting in a smaller radius. Conversely, species with a lower nuclear charge will be larger due to reduced attraction on the electron cloud. Therefore, within a set of isoelectronic species, the one with the highest nuclear charge is the smallest, while the one with the lowest charge is the largest.