we know electron affinity of the anion should be high for better ionic bond. Electron affinity of S is higher than O.But size of O is less than S(Fazan's rule postulate) .So what will be the answer?????
Here S atom is bigger in size than O atom due to which polarizability of the S atom is more and thus more is the covalent character and thus lesser is the ionic nature. On the other hand, O atom is smaller, thus lesser is covalent character and hence more is the ionic.