What must occur when a chemical change takes place in terms of substances?

When a chemical change occurs, a new substance is formed as a result of the rearrangement of atoms and the breaking and forming of chemical bonds. This transformation distinguishes chemical changes from physical changes, where no new substances are formed, and only the physical state or form may change.

In a chemical reaction, the reactants undergo a transformation that leads to the production of one or more products, which have different properties compared to the original substances. This is why the formation of a new substance is a defining characteristic of chemical changes. For example, when iron rusts, it combines with oxygen to form iron oxide, a completely different compound with distinct properties.

Consequently, the other options do not accurately describe what happens during a chemical change: no substances are solely unaffected, only the form changing indicates a physical change, and rearranging to form the same substance does not yield new materials but merely restates the original, which contradicts the essence of a chemical transformation.