Displacement reaction is a chemical reaction in which a more reactive metal displaces a less reactive metal from its salt solution.
Eg :- if we take dilute copper sulphate solution (blue in colour) and place an iron nail in it and stir the solution... After a few minutes the nail becomes red-brown. This is because a layer of copper gets deposited over the surface of the nail.
The colour of solution slowly changes from blue to green due to the formation of iron sulphate ......
This activity shows that iron displaces copper from copper sulphate solution