* Double Displacement: In this type of reaction, the positive and negative ions of two reactants switch places.

* Metathesis: This is another term for double displacement, emphasizing the exchange of ions.

Let's break down the reaction:

* Reactants: HgCl₂ (mercuric chloride) and H₂S (hydrogen sulfide)

* Products: HgS (mercuric sulfide) and 2HCl (hydrochloric acid)

In this reaction:

* The mercury (Hg²⁺) ion from HgCl₂ combines with the sulfide (S²⁻) ion from H₂S to form HgS.

* The hydrogen (H⁺) ions from H₂S combine with the chloride (Cl⁻) ions from HgCl₂ to form HCl.

In essence, the cations and anions swap partners, resulting in the formation of new compounds.