A displacement reaction is a reaction in which a more reactive element displaces a less reactive element from its compound. The elements at the top in the activity series can replace the elements at the bottom.

Example: Zinc is more reactive than copper and replaces copper from copper sulphate as:

\(CuSO_{4(aq)}+Zn_{(s)} \rightarrow ZnSO_{4(aq)}+Cu_{(s)}\)

Double displacement reaction is the type of reaction where two compounds react in the way
that there is exchange of positive and negative ions and new compounds are formed as
products.

Example: On mixing sodium sulphate solution with barium chloride solution, a white precipitate of barium sulphate is formed as:

\(Na_2SO_{4(aq)}+BaCl_{2(aq)} \rightarrow BaSO_{4(s)}+2NaCl_{(aq)}\)