The reaction in which the place of the ion of a less reactive element in a compound is taken by another more reactive element by the formation of its own ions is called displacement reaction.
When zinc granules are added to the blue coloured copper sulphate solution, the zinc ions formed from zinc atoms take the place of C2+ ions in CuSO4, and copper atoms, formed from Cu2+ ions comes out i.e. the more reactive zinc displaces the less reactive Cu from copper sulphate.
