An ion exchange resin is a polymer with a charged "functional group" that is used to purify liquids like water by exchanging unwanted ions for desirable ones. These tiny, porous beads are commonly used in water softening, demineralization, and other purification processes across industries like food processing, power generation, and medicine. The resin's fixed charge attracts ions of the opposite charge, swapping them out for a different ion held on the resin bead.