Both acids and bases contain hydrogen ions and hydronium ions. It is the ratio between these two types of ions which decides whether a sloution is an acid or a base. In an acid, there are more hydrogen ions than hydronium ions, whereas in base there are more hydronium ions as compared to hydrogen ions. The presence of both hydrogen and hydronium ions at the same time results from the dissociation of small amount of water molecules preseent in acids and bases.