Epoxy resins (epoxide polymers): select the statement that correctly describes a core chemical feature or processing trait of epoxy systems.

Introduction / Context:
Epoxy resins are versatile thermosetting systems used in coatings, adhesives, laminates, and composites. Understanding their functional groups and curing chemistry ensures correct selection of hardeners and processing windows.

Given Data / Assumptions:

• Common epoxies are diglycidyl ethers (e.g., DGEBA) bearing terminal epoxide (oxirane) groups.
• Curing (with amines, anhydrides, etc.) converts these reactive ends into a crosslinked network.
• Manufacture involves step-growth reactions (not solely addition), and prepolymers are not crosslinked until cure.

Concept / Approach:
The defining feature is the epoxide ring functionality at chain ends or along the backbone, enabling room-temperature or elevated-temperature curing. Prior to cure, epoxies are oligomeric liquids/solids with epoxy equivalents; after cure, they form a thermoset network. Emulsion polymerisation is not the primary production route.

Step-by-Step Solution:
Identify signature chemistry: terminal epoxy groups.Eliminate claims of “only addition” and “already crosslinked.”Reject emulsion polymerisation as the typical route.

Verification / Alternative check:
Technical datasheets specify epoxy equivalent weight (EEW), reflecting epoxide groups per mass prior to cure.

Why Other Options Are Wrong:
(a) and (d) misstate mechanisms and methods; (c) describes the post-cure state, not the resin as supplied.

Common Pitfalls:
Confusing epoxy “resin” (prepolymer) with the cured epoxy “thermoset.”

Final Answer:
Contain epoxy groups at the ends of the polymer chain prior to cure.