What term describes a material that changes from one atomic structure to another when heated and cooled?

What term describes a material that changes from one atomic structure to another when heated and cooled?

• A. Allotropy
• B. Polymorphism
• C. Phase transformation
• D. Heat treatment

Answer: (A)

Allotropy is the phenomenon where an element exists in more than one crystalline form and can switch between those forms as conditions like temperature or pressure change. This matches the idea of a material changing its atomic structure when heated and cooled. For example, carbon can appear as graphite or diamond, and iron changes its crystal arrangement with temperature. Polymorphism is similar but usually refers to compounds rather than elements. Phase transformation and heat treatment describe the process or the overall category of changes, not the specific case of a single element adopting different atomic structures. So allotropy best fits the description.