Which statement describes a chemical reaction?

A chemical reaction is a process that leads to the transformation of one set of chemical substances to another.

The answer would be 'reactants form products when atoms are rearranged.' (Even though some phase changes, which are physical changes, can fall underneath this, that would be the correct answer mostly applied to chemical reactions.) By the Law of Conservation, No energy or amounts of matter could be created or destroyed, therefore nothing is lost nor gained. Reactants are the items that are technically reacting whilst the product is the outcome. Products don't react.