Here's how to determine the oxidation state of chlorine in the chlorate ion (ClO₃⁻):

1. Know the Oxidation State Rules:

* Oxygen usually has an oxidation state of -2 (except in peroxides and superoxides).

* The sum of the oxidation states in a polyatomic ion equals the charge of the ion.

2. Apply the Rules:

* We have three oxygen atoms, each with an oxidation state of -2, for a total of -6.

* The overall charge of the chlorate ion is -1.

* To balance this, the chlorine atom must have an oxidation state of +5.

3. Conclusion:

The oxidation state of chlorine in the chlorate ion (ClO₃⁻) is +5.