Svante Arrhenius, in 1884-1887, showed that electrolytes dissolve to give ions in solution. There was a problem, starting in the mid-1880s. The explanation for why strong electrolytes behaved the way they did was first suggested in 1904, but was not proven until 1923. The molecule, as such, does not exist in solution. The only thing present are ions.
Sodium chloride is an example of a strong electrolyte.
NaOH is another. Now, having said that, if the solution is sufficiently concentrated, you form what are called ion pairs. Not molecules, mind you. HClO 4 perchloric acid You ought to memorize this list, because almost every other acid is weak. The most common example used by teachers is HCl.