The compound that is not a constituent of the electrolytic mixture used in the Hall-Heroult's process is:

NaAlO₂

Reason — In the standard Hall-Heroult process, the electrolytic mixture consists of 20% alumina (Al₂O₃), 60% cryolite (Na₃AlF₆) and 20% fluorspar (CaF₂). Hence, NaAlO₂ is not a part of the electrolytic mixture.