The correct answer is: here are 10 clear examples of physical change.
- Melting ice (solid water → liquid water) — reversible
- Freezing water (liquid water → solid ice) — reversible
- Boiling water (liquid → gas/steam) — reversible by condensation
- Condensation of steam (gas → liquid) — reversible
- Sublimation of dry ice (solid CO2 → gas) — reversible by deposition under appropriate conditions
- Dissolving sugar in water (sugar dispersed in water) — usually reversible by evaporation/crystallization
- Crushing an aluminum can (change of shape/size) — usually reversible only by reshaping, but still physical
- Cutting or tearing paper (change in shape/size, no new substance) — irreversible but physical
- Stretching a rubber band (elastic deformation) — often reversible if within elastic limit
- Mixing sand and salt (forming a mixture; components retain identity) — reversible by physical separation (e.g., dissolving salt then filtering)
Explanation
A physical change alters physical properties (shape, phase, size, texture, or arrangement) without producing new chemical substances. Key signs of a physical change include changes of state (melting, freezing, boiling, sublimation), deformation (cutting, crushing, bending), or mixing/dispersing where the original materials retain their chemical identity (dissolving, mixing).
Notes and distinctions:
- Reversibility is common but not required for a change to be physical. For example, melting is reversible, while shredding paper is not easily reversed—even though both are physical changes.
- Dissolving is typically a physical change (sugar + water → sugar solution). It becomes chemical only if a chemical reaction occurs (e.g., acid reacting with metal).
- Breaking glass is a physical change (no new substance), though it may appear dramatic.
- To decide chemical vs physical: ask whether the molecular identity of substances changed (new bonds/compounds formed) — if yes, it’s chemical; if just shape/phase/mixture changed, it’s physical.