Reactivity describes a material's propensity to release energy or undergo what?

• A. Heat
• B. Decay
• C. Phase shift
• D. Change

Answer: (D)

Reactivity is about how readily a material participates in chemical reactions—its tendency to undergo a chemical change when it encounters another substance or the right conditions. That change may release energy (exothermic) or absorb energy (endothermic), or simply form new substances. Among the options, change best captures the concept because reactivity is about undergoing a chemical transformation. Heat describes a possible outcome of such a reaction, but not the tendency itself; decay is a specific process for certain materials; phase shift is a physical change that doesn’t necessarily involve a chemical reaction.