In electrochemical reaction of Cu+Mg2+, the metal displacement will not take place. Displacement reactions occurs when a metal from the electrochemical series is mixed with the ions of metal lower down in the series. In the electrochemical series Mg is placed above Cu. Hence, metal displacement reaction won't occur inCu+Mg2+.InPb+Ag+ and Zn+Cu2+, lead and zinc are more reactive than silver and copper, hence they can displace silver and copper respectively from their salt solution.