The correct option is (c) dextran-polyethylene glycol
The best explanation: The most thoroughly investigated two-phase aqueous system is dextran-polyethylene glycol system. In this system, dextran forms the more hydrophilic, denser, lower phase and polyethylene glycol the more hydrophobic, less dense, upper phase. In potassium phosphate buffer-polyethylene glycol system, the polymers form the upper hydrophobic phase. Agar-starch was noted as a two-phase system for the first time by Beijerinck in 1896. Sodium carbonate- polyethylene glycol is another such system used during downstream processing mainly in biotechnological and chemical industries.