Which of the following would indicate a displacement reaction?

• A. Gas is evolved
• B. Colour change, metal coating, or formation of a solid
• C. Solution becomes perfectly clear with no change
• D. Temperature decreases without other changes

Answer: (B)

In a single-displacement reaction, a more reactive element pushes a less reactive one out of a compound, forming new products. The clearest signs are when you actually see something new forming: a color change in the solution, a metal coating appearing on the surface of the metal, or the formation of a solid (precipitate). These visuals show that a new substance has been produced as the reaction proceeds. Gas production and temperature changes can occur in other kinds of reactions as well and aren’t definitive proof of displacement on their own. So the presence of a color change, a metal coating, or a solid forms the strongest indicator that a displacement reaction is occurring.