Which is the correct term for a substance reacting adversely with another?

The term that best describes a substance reacting adversely with another is "corrosive." A corrosive substance has the ability to cause damage or destruction when it comes into contact with another material, often leading to chemical reactions that can degrade or destroy the material. This can happen through processes such as oxidation or chemical erosion, which are significant in various contexts, including chemistry and fire safety.

Other terms like "stable" and "unstable" refer to the behavior of substances in terms of their physical or chemical constancy. A stable substance doesn’t easily change or react, while an unstable one may readily undergo changes or reactions. Inert refers to substances that do not readily engage in chemical reactions, meaning they remain largely unaffected in diverse chemical environments. Thus, while "unstable" might imply a readiness to react, it doesn't necessarily encompass adverse reactions with other substances as "corrosive" does.