Which statement best describes thermoplastic polymers?

• A. Plastics that melt and flow upon heating.
• B. Plastics that only undergo physical changes upon heating and cooling.
• C. Polymers that crystallize on heating.
• D. Plastics that decompose before softening.

Answer: (B)

Thermoplastic polymers are characterized by reversible, physical changes when heated. They soften or melt and can flow, and upon cooling they solidify again, allowing the material to be reshaped without any chemical change to the polymer itself. That ability to be repeatedly melted and reshaped comes from the fact that heating causes physical transitions (like glassy to rubbery to molten states) rather than chemical reactions or crosslinking. The description that best fits this behavior emphasizes that only physical changes occur during heating and cooling, which is why they can be remolded. The other ideas either focus only on melting without noting the reversibility, or suggest processes (like crystallization on heating or decomposition before softening) that don’t define thermoplastics.