You're asking about the oxidation numbers in the perchlorate ion (ClO₄⁻). Here's how to determine them:

* Oxygen (O): Oxygen typically has an oxidation number of -2, and this is true here.

* Chlorine (Cl): To find the oxidation number of chlorine, we use the following:

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

* There are four oxygen atoms, each with a -2 charge, totaling -8.

* Therefore, the oxidation number of chlorine must be +7 to balance out the charge: (+7) + (-8) = -1

In summary:

* Chlorine (Cl): +7

* Oxygen (O): -2