Final answer:
An isoelectronic series includes atoms and ions with the same number of electrons. The size varies depending on the nuclear charge, with species having higher nuclear charge having smaller atomic radii.
Step-by-step explanation:
An isoelectronic series consists of atoms and ions that share the same electron configuration, meaning they have the same number of electrons. The size of these isoelectronic atoms and ions is determined by the number of protons in the nucleus, known as the nuclear charge. Examples of such series include N³-, O²-, F, Ne, Na+, Mg²+, and Al³+ (1s²2s²2p⁶), and P³-, S²-, Cl-, Ar, K+, Ca²+, and Sc³+ ([Ne]3s²3p⁶). In any isoelectronic series, the species with a higher nuclear charge will have a smaller atomic radius due to stronger electrostatic attraction between the nucleus and electrons.