Which adhesive is usually supplied in two parts which must be mixed prior to use?

The correct answer is epoxy resin. This adhesive is typically supplied in two separate components – a resin and a hardener – which must be mixed together prior to application. This two-part system allows for a stronger bond as the chemical reaction between the resin and hardener activates the curing process, resulting in a durable and robust adhesive suitable for various materials and applications.

Silicone rubber is generally supplied as a single component or in a form that requires curing in the presence of moisture, while polyurethane adhesives can be either single or two-part systems but do not require a separate hardener in their most common formulations. Cyanocrylate adhesives are single-component adhesives that bond quickly upon exposure to moisture. Therefore, epoxy resin is distinct in its requirement for mixing two parts to achieve the desired adhesive properties.