___________ refers to a physical or chemical change that requires or is accompanied by the absorption of heat.

• A. Exothermic
• B. Thermal reactivity
• C. Runaway reaction
• D. Endothermic

Answer: (D)

Endothermic processes involve absorbing heat from the surroundings as the change occurs. This means the system must gain energy for the physical or chemical change to proceed, such as melting ice or dissolving certain salts where heat must be supplied or drawn in. Exothermic changes, by contrast, release heat to the surroundings, which is the opposite behavior. A runaway reaction is a hazardous scenario driven by rapid, often exothermic heat production, not heat absorption. The broader idea of thermal reactivity describes how a material responds to heat in general, but it does not specifically define a process that requires or accompanies heat input. So, the term that best matches a change that requires or is accompanied by heat absorption is endothermic.