How is an unstable (reactive) material defined?

An unstable (reactive) material is defined as one that will undergo violent changes when exposed to heat or shock. This definition highlights the nature of such materials, which possess the potential to engage in unanticipated and often hazardous reactions due to external stimuli. For instance, these materials can exhibit behavior such as rapid decomposition, explosive reactions, or the release of toxic gases when subjected to temperature increases or mechanical forces. This is a critical consideration in laboratory settings where the handling of flammable gases is common, as understanding how these materials can react under specific conditions helps ensure safety and effective risk management.

While other choices discuss aspects of material behavior, they do not accurately capture the key characteristic of instability or reactivity which is central to the definition of unstable materials. For example, materials that are prone to combustion at room temperature are not necessarily unstable; they can be stable under specific conditions but still combust under the right circumstances. Similarly, substances that are deemed safe under all conditions or non-interactive compounds do not align with the concept of reactivity and instability at all.