As per Fajan's rule, more is the charge on cation and less is the size of the cation, more is the covalency. Out of Mg2+ and Na+, charge on Mg2+ is more hence, its compound will be more covalent. Similarly, more is the change on anion, more is the size of anion and hence more is the covalent character. O2− has higher charge than Cl−. ∴Mg2+ and O2− combination will have more covalent character.
