Answer :
A precipitate is a water insoluble substance.any reaction that produces a precipitate is called a precipitation reaction. When sodium sulphate reacts with Barium it produces Barium sulphate which is a white precipitate , this precipitate is formed by the reaction of sulphate ion and Barium ion . The other product obtained is sodium chloride which remains in the solution. Here there is an exchange of ions between the reactants so this reaction also be called as double displacement reaction. \( Na_{2}SO_{4}{(aq)} + BaCl_{2}{(aq)}\rightarrow BaSO_{4}{(s)}+2NaCl_{(aq)}\)