Final answer:
The polyatomic ion in HClO3 is the chlorate ion, and HClO3 itself is called chloric acid.
Step-by-step explanation:
The polyatomic ion involved in HClO3 is chlorate, and its name is exactly that, chlorate ion. This ion is part of the oxyanions of halogens, where the central atom (in this case chlorine) is surrounded by oxygen atoms. The ion has the formula ClO3 and carries a -1 charge, indicating it has one more electron than protons. In the naming convention for oxyanions, the acid form, which contains additional hydrogen atoms, follows specific nomenclature rules based on the number of oxygen atoms present. Therefore, HClO3 is named chloric acid, devoid of any prefixes like 'per-' or 'hypo-' that are used in other members of the halogen oxyanion series, such as perchloric acid (HClO4) or hypochlorous acid (HClO).