PDF Polyatomic Ions List And Worksheet Answer Key ions remain intact, and parentheses may be required when using subscripts. For example, ammonium chloride is NH 4 Cl and ammonium sulfide is (NH 4) 2 S. Ammonium is the only polyatomic cation. Common anions are shown in Table 1. Dr. Scott Beaver Page 1 of 6 Table 1. Polyatomic ions Nomenclature for polyatomic ions Worksheet-Answer Key