This is a precipitation reaction: HgI2 is the formed precipitate.
Reactants:
HgCl2 – Mercury(II) chloride, Mercury dichloride
Other names: Mercuric chloride, Corrosive sublimate, ClHgClSulema, Corrosive mercury chloride, Mercury bichloride, Mercury perchloride, HgCl2, Mercuric bichloride, Sublimate, Dichloromercury, Perchloride of mercury, Sublimat, Dichlorure de mercure, Hydrargyrum bichloratum, Chlorure mercurique, Bichlorure de mercure, Quecksilber(II)-chlorid, Mercury (II) chloride
Appearance: Colorless or white solid ; White crystals or powder
KI
Names: Potassium iodide, KI, ThyrosafeThyroshield, Iosat, Kaliumiodid, Nukepills, Potassium Iodide
Products:
HgI2 – Mercury(II) iodide
Other names: Mercury diiodide, Mercuric iodide, Red mercury (α form only)Coccinite (α form only), Mercury Diiodide, Red mercuric iodide, Mercuric iodide red, Hydrargyrum bijodatum, Mercuric iodide, red