Which of the following statements about thermoplastic material is correct? They

Step 1: Analyze the question The question asks which statement correctly describes thermoplastic materials, so we need to recall how they behave when heated.

Step 2: The concept Plastics fall into two main groups based on how they respond to heat:

• Thermoplastics have long polymer chains held together by relatively weak intermolecular forces. Heating weakens these forces, so the plastic softens and melts. On cooling, it hardens again. This process can be repeated, so they can be remolded and recycled. Examples: polyethene (polythene), PVC, polystyrene, nylon.
• Thermosetting plastics (thermosets) have strong cross-links between chains. Once set, they do not soften or melt on reheating. Strong heating makes them char or decompose. Examples: Bakelite, melamine, urea-formaldehyde.

Step 3: Evaluate the options

• A. Do not melt on heating: This describes thermosetting plastics, so it is wrong.
• B. Harden on heating: This also describes thermosets, which harden permanently when first heated and cured. It is wrong for thermoplastics.
• C. Decompose on heating: Thermosets tend to char or decompose rather than melt. Thermoplastics melt first, so this is wrong.
• D. Soften and melt on heating: This is correct. The weak intermolecular forces break down on heating, so the material softens and melts.

Answer: D

Exam tip: Remember the names. Thermo-PLASTIC means it stays plastic (moldable) when heated, so it can be reshaped again and again. Thermo-SETTING means it sets permanently, like cement, and cannot be remelted. Think of a plastic bucket that can be melted and recycled (thermoplastic) versus a Bakelite socket that never melts (thermoset).