Polymorphism refers to what?

• A. A material has more than one crystal structure
• B. A material has multiple compositions
• C. A material has different densities
• D. A material has different crystal sizes

Answer: (B)

Polymorphism is when a material with the same chemical formula can crystallize in more than one distinct arrangement of atoms, i.e., different crystal structures. This matters because the way atoms are packed in the lattice changes properties like hardness, density, and optical behavior, even though the composition is unchanged. For example, carbon can exist as diamond or graphite—same element, very different bonding and structure. Titanium dioxide also has different polymorphs (rutile and anatase) with different properties. The idea is about structure, not composition, so having multiple compositions would describe something else entirely, not polymorphism.