The First thing that you must knew about Electrolyte Solution, Have the Criteria:
- The Solution that Perfect Ionized 
- Strong Acid or alkali (have strong electrolyte) and weak Acid or alkali (have Weak Elektrolytes)
- Salt Solution (NaCl, KCl, and any others)

I thing Molten Napthalena Is the best Answer, Napthalena as an Organic coumpund has a Stabilized structur, so dificult to ionized.

I Hope that answer your question...