A ________ is a highly efficient ion-exchange process in which resin is regenerated with sulfuric acid in the first vessel and caustic soda in the second vessel

• A. softener
• B. distiller
• C. adsorber
• D. demineralizer

Answer: (D)

Demineralization uses a two-bed ion-exchange process. Water first passes through a cation resin, which removes positively charged ions and releases hydrogen; this resin is regenerated with sulfuric acid. It then goes through an anion resin, which removes negatively charged ions and releases hydroxide; this resin is regenerated with caustic soda. The combination of these two regenerants restores the resins and yields water with most mineral ions removed. Other options don’t fit because a softener targets hardness with brine, a distiller relies on evaporation, and an adsorber is a general term not describing this two-vessel, two-regenerator ion-exchange setup.