An ionic compound is formed between a metal and a non metal. The metal being electropositive can form a cation by transferring the electron to the electronegative non metal that gains the electrons to form an anion. Both the elements try to get a stable octet configuration by the transfer of electrons. The number of electrons lost by metal will be equal to the number of electrons gained by the non metal. Hence, the magnitude of positive charge on the cation will be equal to the magnitude of negative charge on the anion. Therefore, the overall charge on the compound will be 0
So the correct answer is the sum of all charges in the formula for an ionic compound is 0