The selenium ion is represented as Se4+, Barium ion is represented as Ba2+ and Phosphorus occurs as phosphate ion i.e., PO43-.
The chemical species that contains a positive charge is known as cation while the chemical species consisting of a negative ion is known as anion.
Selenium is a metal, therefore is exist as a cation with Se4+ representation having +4 charge. Barium is a metal, thus it exist as a cation with Ba2+ representation having +2 charge while phosphorus always occurs as a phosphate ion i.e., PO43- which is an anion as phosphorus is a non-metal.
Therefore, the representation of the ions are given above.
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