Which change results in the formation of new substances?

A chemical change is defined by the formation of new substances through the rearrangement of atoms during a chemical reaction. This process involves breaking and forming chemical bonds, leading to the production of substances that have different properties from those present before the change.

For instance, when iron rusts, it reacts with oxygen in the environment to create iron oxide, a new substance with different characteristics from elemental iron. In a chemical change, these transformations are often indicated by evidence such as color changes, gas release, or the formation of a precipitate, clearly demonstrating that different substances have been created.

Other types of changes, such as physical or mechanical, do not lead to the formation of new substances. Physical changes, like melting or boiling, involve changes in the state of matter or physical form while keeping the chemical identity intact. Mechanical changes typically involve a physical alteration, such as grinding or mixing, which also does not result in new substances. Electrical changes, while they may involve energy transformations, similarly do not imply the creation of new chemical entities unless a chemical reaction occurs as a result.

Thus, the formation of new substances distinctly characterizes a chemical change, making it the correct choice.