How would you explain that BaO is insoluble but BeSO4 is soluble in water?
BaO and BaSO4 are ionic compounds. Further the size of O2– ion is much smaller as compared to that of SO42– ion. Also, a bigger anion stabilises a bigger cation more than a smaller anion stabilises a bigger cation. As a result lattice enthalpy of BaO is much less than that of BaSO4 and hence BaO is insoluble in water while BaSO4 is soluble.