Ion-exchange materials: strong acid cation exchangers used in water treatment are commonly made from which resin family?

Introduction / Context:
Cation exchange resins are functionalised polymers bearing fixed acidic groups that exchange cations with the surrounding solution. Although modern plants overwhelmingly use sulfonated styrene–divinylbenzene resins, classic materials and many exam syllabi also include sulfonated phenolic (phenol–formaldehyde) resins as cation exchangers. The question targets recognition of that resin family among generic options.

Given Data / Assumptions:

• Focus is on the resin family historically used for cation exchange.
• Functional groups are sulfonic acids for strong acid cation exchangers.
• Options list broad resin chemistries rather than specific copolymers.

Concept / Approach:
Phenol–formaldehyde resins can be sulfonated to introduce –SO3H groups, creating strong acid cation exchangers. Urea/melamine amino resins and epoxies are thermosets used for adhesives and coatings, not typical ion-exchange backbones. While sulfonated styrene–DVB is more common industrially today, within the offered families the correct classical answer is the sulfonated phenolic resin.

Step-by-Step Solution:

Verification / Alternative check:
Water-treatment texts list phenolic cation exchangers alongside styrene–DVB resins, confirming historical and educational relevance.

Why Other Options Are Wrong:

• Urea/melamine: amino resins used in laminates/wood adhesives.
• Epoxy: structural adhesives/coatings.
• Acrylic latex: film-forming binders, not ion exchangers.

Common Pitfalls:
Assuming only styrene–DVB exists; older phenolic exchangers remain part of exam content.

Final Answer:
Phenolic resin (sulfonated phenol–formaldehyde)