Thank you for posting this question! So here, the best way to do this is to think about what you need for an electric current. For an electric current, you need flow of charge. Therefore, you need something in solution that is charged or that can help with the flow of charge. Here, the answer molecules is too vague -- you need to specify a type of molecule. Although acids and bases might be tempting because they form charged molecules, not all acids and bases have strong negative or positive charges. For example, weak acids and bases will likely be in a mostly uncharged state. Therefore, the best answer here is "ions." Ions are molecules that are charged, but we use the word ion to describe all charged particles. Ions have the permanent charges we need to be able to have an electric current.