Thermosetting plastics do not melt or remould on heating that's why option'A' which is thermosetting plastics is the correct option.

Thermosetting Plastics

Thermosetting plastics are a type of plastic that undergoes a chemical change when heated and molded, and they cannot be remolded again on heating. These plastics have a cross-linked molecular structure that forms a rigid and inflexible network. This cross-linking is irreversible and gives thermosetting plastics their unique properties.

Properties of Thermosetting Plastics:
- Rigidity: Thermosetting plastics are rigid and do not easily deform under pressure or heat.
- High Heat Resistance: These plastics can withstand high temperatures without melting or softening.
- Chemical Resistance: Thermosetting plastics are resistant to many chemicals, making them suitable for various industrial applications.
- Electrical Insulation: Due to their high heat resistance and non-conductive properties, thermosetting plastics are used as electrical insulators.
- Strength: These plastics have excellent mechanical strength and can withstand heavy loads and stress.

Examples of Thermosetting Plastics:
- Epoxy Resin: Epoxy resin is commonly used in adhesives, coatings, and composites. It has excellent chemical resistance and high mechanical strength.
- Phenolic Resin: Phenolic resin is widely used in electrical components, automotive parts, and household appliances due to its excellent insulation properties.
- Polyester Resin: Polyester resin is used in boat building, automotive parts, and construction due to its high strength and corrosion resistance.

Difference between Thermosetting Plastics and Thermoplastics:
- Thermosetting plastics, as mentioned earlier, cannot be remolded once they are heated and set. In contrast, thermoplastics can be melted, reshaped, and remolded multiple times without undergoing any chemical change.
- Thermoplastics have a linear or branched molecular structure, which allows them to be melted and reshaped repeatedly. They become soft and pliable when heated and solidify when cooled.
- Unlike thermosetting plastics, thermoplastics can be recycled as they retain their original properties even after multiple heating and cooling cycles.

In conclusion, thermosetting plastics are a specific type of plastic that cannot be remolded on heating. They have a cross-linked molecular structure, making them rigid, heat-resistant, and chemically resistant. Examples of thermosetting plastics include epoxy resin, phenolic resin, and polyester resin.