What observable evidence indicates a reaction between acids and metals?

• A. Fizzing and gas identification.
• B. Color change only.
• C. Odor change only.
• D. No observable change.

Answer: (A)

When acids react with metals, you usually see fizzing as bubbles form in the solution. That fizzing comes from hydrogen gas being produced as the metal reacts with the acid. You can test the gas by collecting it and bringing a lit splint near it—the characteristic squeaky pop confirms hydrogen. Often the reaction also feels warm because it’s exothermic, and the metal may dissolve into the solution. Colors changing or odors changing aren’t reliable indicators for this type of reaction, and saying there’s no observable change isn’t accurate because the gas bubbles provide clear evidence.