How do you determine if a polyatomic ion needs to be counted together?

Calculate from Oxidation Number

The oxidation number of oxygen is -2, and the oxidation number of hydrogen is +1. Add together the oxidation numbers of all the atoms in the polyatomic ion. In the example, -2 +1 = -1. This is the charge on the polyatomic ion.

passing a magnet thought the

mixture , because iron gets attracted to magnet .