What is the oxidation number for all elements of ClO2-?

Cl = +3 and O = -2

##ClO_2^(-)## is a polyatomic ion with a charge of -1

The charge of chlorine is: +3 The charge of each oxygen is: -2

So how do you figure this out?

Oxygen always has a charge of -2. Since there are two oxygens, the amount of negative charge from those oxygens is -4 (-2 x 2)

The charge of the chlorine must cancel some of the negative charge of the oxygens, except for the overall charge of the ion. (+3 and -4 = -1) So you can determine that the chlorine must have a charge of +3

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