Which scenario is a chemical change?

• A. Ice melts to water
• B. Iron rusts
• C. Cutting paper
• D. Dissolving sugar in water

Answer: (B)

When a chemical change happens, a substance actually becomes a different material with new properties. Iron rusting is an example because iron reacts with oxygen (and often water in the air) to form iron oxide, a substance different from the original iron. The change involves breaking and re-forming chemical bonds, and the product has a different composition, so the process is not easily reversed by simple physical means.

Melting ice to water is a physical change—water stays H2O, but changes state. Cutting paper is also physical—it's just changing size or shape, not its identity. Dissolving sugar in water is typically considered a physical change too, since the sugar is dispersed but still the same substance, and you can usually recover the sugar by evaporation.