Iodide ion ($I^-$) is the conjugate partner of $HI$.
Work Step by Step
1. Identify if the substance is an acid or a base (or both): - HI is an acid. 2. Since $HI$ is an acid, remove one proton from it: - Remove one hydrogen and subtract one from the charge: $HI -- \gt I^-$ - This is the conjugate base of $HI$. 3. Name it: Ions of nonmetals from group $VII$ receive an "ide" to the name of the element stem name: $I$ = "Iod" Ion: Iodide.