State the $IUPAC$ name of the following complex: Nessler's reagent.

(N/A) Nessler's reagent is the chemical compound $K_{2}[HgI_{4}]$.
In this complex,the central metal ion is mercury $(Hg)$ with an oxidation state of $+2$.
The ligand is iodide $(I^-)$,which is named as 'iodido' in the $IUPAC$ system.
Since there are four iodide ligands,the prefix 'tetra' is used.
The complex anion is $[HgI_{4}]^{2-}$,which is named as 'tetraiodidomercurate$(II)$' because the metal is part of an anionic complex.
Combining these,the full $IUPAC$ name is Potassium tetraiodidomercurate$(II)$.