Reactivity in science refers to how various chemicals participate in chemical reactions when they are exposed to other substances. A chemical that reacts easily with other substances is considered highly reactive.
One example of a reactive material is magnesium, which burns brightly when heated. In contrast, platinum does not burn when heated and it is considered non-reactive. Other chemicals that have little reactivity include gold and silver. Potassium, sodium and calcium rank near the top of most-reactive materials. Some chemicals react together so strongly that they create a new substance called a compound. A common example of a compound formed through reactivity is water, formed when hydrogen and oxygen react.