Which of the following indicates a chemical change?

• A. Alterations with color change, heat emission, bubbles, or solid formation.
• B. Dissolving a substance in water.
• C. Change of state from solid to liquid.
• D. Breaking a glass.

Answer: (A)

Detecting chemical changes hinges on signs that substances are actually new ones formed, not just altered in appearance. When a reaction occurs, you often see color changing, heat being released or absorbed, gas bubbling, or a solid forming from solutions. Each of these indicates a rearrangement of atoms into different substances, and often a measurable energy change accompanies it.

That’s why the option listing color change, heat emission, bubbles, or solid formation is the best match: these are classic indicators that a chemical reaction is taking place and new materials are created. In contrast, dissolving a substance in water is typically a physical change where the substance is dispersed but not chemically transformed; a change of state (solid to liquid) is physical as well, since it changes form but not the substance’s identity; breaking a glass is a mechanical change, not a chemical one.