So if the charge, let's say we're dealing with sodium ions, the Z value is plus one. If we're dealing with chloride ions, the Z value is negative one. If we're dealing with, let's say potassium has a positive one, it's also positive one, and so forth. So basically, Z is the charge on the ion. It could be positive negative one, positive negative two, positive negative three. Now, if we're dealing with an uncharged neutral molecule, z is zero.