The reaction in which there is an exchange of ions between the reactant takes place is called double displacement reaction.

For examples:

Na₂SO₄ + BaCl₂→ BaSO₄ + 2NaCl

Sodium Barium Barium Sodium

sulphate chloride sulphate chloride

AgNO₃ + NaCl → AgCl + NaNO₃

Silver Sodium Silver Sodium

nitrate chloride chloride nitrate