A displacement reaction occurs when a more reactive metal displaces a less reactive metal from its salt solution. According to the activity series, copper is more reactive than silver. Therefore, when copper is placed in silver nitrate solution, it displaces silver: Cu(s) + 2AgNO₃(aq) → Cu(NO₃)₂(aq) + 2Ag(s). In other options, the metals are less reactive than the metal in the salt solution, so no displacement occurs.