Answer: The balanced chemical equation is written below.
Step-by-step explanation:
Double displacement reaction is defined as the chemical reaction in which exchange of ions takes place.

The chemical equation for the reaction of potassium iodide and mercury (II) chloride follows:

By Stoichiometry of the reaction:
2 moles of potassium iodide reacts with mercury (II) chloride to produce 1 mole of mercury (II) iodide and 2 moles of potassium chloride
Hence, the balanced chemical equation is written above.