Final answer:
The name for HgCl₄ is mercury(II) chloride, where the Roman numeral (II) indicates the +2 oxidation state of mercury in this compound.
Step-by-step explanation:
The name for HgCl₄ is mercury(II) chloride. The Roman numeral (II) indicates that mercury has a +2 oxidation state. In this compound, one mercury atom is bonded with four chloride ions, each with a -1 charge. The sum of the charges of the chloride ions (-4) must balance the charge of the mercury ion (+2), which means that there are in fact two mercury ions to match the four chloride ions, hence the mercury is in the +2 oxidation state. Though the formula might suggest a single mercury atom with a +4 charge, this is not accurate, as mercury does not commonly form a +4 oxidation state. The correct name reflects that there are two mercury ions, each with a +2 charge.