Give reasons for the following: (a) size of a Cation is smaller than its parent atom. (b) Size of an anion is larger than its parent atom. (c) Radius of argon is greater than that of chlorine. (d) Be and Al show similar properties. (e) The first electron affinity of oxygen is positive but the second electron affinity is negative. (f) The difference of atomic size between lithium and beryllum is much greater than between sodium and magnesium.

The sizes of ions compared to their parent atoms are influenced by changes in fundamental properties such as electron shielding and effective nuclear charge when an electron is either added or removed to form the ions. The atomic radius comparison between Argon and Chlorine, as well as the atomic size difference of Lithium and Beryllium versus Sodium and Magnesium, can be understood in light of their positions in the periodic table and the variation in nuclear charge and shielding effect. Elements in the same group of the periodic table like Beryllium and Aluminum exhibit similarity in properties due to comparable electron configurations. The variance in oxygen's first and second electron affinities is because of electron-electron repulsion that increases energy requirement.