Final answer:
The polyatomic ions with a 2- ionic charge from the options provided are sulfate (SO4^2-) and phosphate (PO4^3-). These ions are examples of oxyanions, where 'ate' suffix indicates more oxygen atoms than their 'ite' counterparts.
Step-by-step explanation:
The student asked which of the following polyatomic ions has a 2- ionic charge: sulfate, nitrate, hydroxide, nitrite, or phosphate. The correct answer is sulfate (SO42-) and phosphate (PO43-). These ions are part of a group known as oxyanions, which are oxides of nonmetals that are molecular ions. Sulfate and phosphate are examples of oxyanions with the suffix '-ate,' which signifies that these ions have more oxygen atoms compared to their '-ite' counterparts. For instance, sulfate (SO42-) contains four oxygen atoms, whereas its counterpart, sulfite (SO32-), contains one less. In contrast, nitrate (NO3-) has a 1- charge and therefore does not meet the criterion of having a 2- charge as mentioned in the question.
It is important to memorize the formulae and charges of these polyatomic ions to understand their role in forming compounds, such as Na2SO4 for a compound of sodium and sulfate, and Ca(NO3)2 for a compound of calcium and nitrate.