Here's why:

* Polyatomic ion: A polyatomic ion is a group of two or more atoms that are covalently bonded together and carry a net positive or negative charge.

* Thiosulfate ion: The thiosulfate ion contains two sulfur atoms and three oxygen atoms, all covalently bonded, and has a net negative charge of 2.

Let me know if you would like to know more about polyatomic ions or the thiosulfate ion!