A teacher wants to perform a classroom demonstration that illustrates both chemical and physical changes. Which would be the best demonstration that she could use to illustrate both the changes?

A bike rusting is an example of a chemical change since rusting is a chemical reaction. New substances are formed from this reaction. On the other hand, other choices given are just physical changes because only the shape or the physical form of the substances are being changed. An example of a physical change is cutting a paper.