Which type of change does not alter the substance's identity?

Which type of change does not alter the substance's identity?

• A. Physical change
• B. Chemical change
• C. Nuclear change
• D. Biological change

Answer: (A)

Physical change happens when a substance changes form or state without changing what it is made of. The molecules stay the same, only their arrangement or energy changes. For example, ice melting into water is still water (H2O); the substance’s identity hasn’t changed, just its phase. Crushing a copper wire or bending a metal also changes shape, not the material itself. Even dissolving a substance in a solvent is typically a physical change because no new substance is formed and the original chemical identities remain. In contrast, chemical changes produce new substances with different properties—like wood burning to ash and gases or iron rusting into iron oxide. Nuclear changes alter the nucleus of an atom and can change the element itself, which is a different kind of transformation. Because physical changes preserve the substance’s identity, they’re the type described in this question.

Physical change happens when a substance changes form or state without changing what it is made of. The molecules stay the same, only their arrangement or energy changes. For example, ice melting into water is still water (H2O); the substance’s identity hasn’t changed, just its phase. Crushing a copper wire or bending a metal also changes shape, not the material itself. Even dissolving a substance in a solvent is typically a physical change because no new substance is formed and the original chemical identities remain. In contrast, chemical changes produce new substances with different properties—like wood burning to ash and gases or iron rusting into iron oxide. Nuclear changes alter the nucleus of an atom and can change the element itself, which is a different kind of transformation. Because physical changes preserve the substance’s identity, they’re the type described in this question.