The following diagram represents an aqueous solution formed by dissolving a sodium salt...

The following diagram represents an aqueous solution formed by dissolving a sodium salt of a weak add in water. The diagram shows only the Na⁺ ions, the X^- ions, and the HX molecules. What ion is missing from the diagram? If the drawing is completed by drawing all the ions, how many of the missing ions should be shown? [Section 16.9]