What evidence can indicate that a displacement reaction has occurred?

• A. Colour change, metal coating, or formation of a solid.
• B. Only a loud sound is produced.
• C. Temperature decreases for all cases.
• D. Change in pH alone.

Answer: (A)

Displacement reactions involve a more reactive metal taking the place of a less reactive one in a compound, and they often produce observable changes. The best signs are a color change in the solution as metal ions are replaced, the formation of a solid metal, or a visible coating of metal on the surface where the reaction is occurring. These indicate new substances have formed and deposition or precipitation has taken place. A loud sound, a temperature drop in all cases, or a change in pH alone aren’t reliable indicators of displacement reactions, so they aren’t good evidence by themselves.