In a single-replacement reaction, which metal can displace another from a compound?

• A. A less active metal
• B. A more active metal
• C. A noble metal
• D. A metal lower in the activity series

Answer: (B)

Activity series and single-displacement reactions show that a more active metal can displace a less active metal from a compound. The reason is oxidation–reduction: the more active metal is more easily oxidized, so it donates electrons to the metal cation in the compound, reducing it to the solid metal while the other metal is released as ions. This redox-driven process only happens when the incoming metal is more active than the metal already in the compound. A less active metal cannot push out a more active one, and a noble metal is typically too unreactive to displace another metal under normal conditions. For example, zinc can replace copper in copper sulfate, forming zinc sulfate and copper metal. So the metal that can displace another from a compound is the more active metal.