Balance the reaction of plumbate ions and hydrochlorite ions:

Pb(OH)42-(aq) + ClO-(aq) → PbO2(s) + Cl-

I put:
Pb(OH)3-(aq) + ClO-(aq) → PbO2(s) + Cl-(aq) + H2O(l) + OH-(aq)

It said: The reaction described in your answer is not balanced. One or more of your reactants appear to have an improper oxidation state. One or more of your products contains an improper oxidation state.

Oxidizing agent: Pb(OH)4^2-
It said: Your answer contains an improper oxidation state. Your answer contains an incorrect or incomplete chemical formula.

Reducing agent: ClO-
Your answer differs too much from the expected answer to provide useful feedback.

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What did I do wrong?

The plumbate ions I know are of the hydrated form Pb(OH)62-

That stuck out at me, but it was in the problem. How did you get to Pb(OH)3-1

So I cant help you with the grader on this, I don't know what the problem is.

To balance the given reaction, it is important to determine the correct oxidation states of the elements involved and then adjust the coefficients to achieve an equal number of atoms on both sides of the equation.

Let's analyze the reaction and determine the oxidation states:

In Pb(OH)42-, the overall charge of the compound is 2-, so the sum of individual oxidation states should equal -2:
Let the oxidation state of Pb be x:
4(-2) + x - 8 = -2
-8 + x - 8 = -2
x = +6
Therefore, the oxidation state of Pb in Pb(OH)42- is +6.

In ClO-, the overall charge of the compound is 1-, so the sum of individual oxidation states should equal -1:
Let the oxidation state of Cl be x:
x + (-2) = -1
x = +1
Therefore, the oxidation state of Cl in ClO- is +1.

By comparing the oxidation states, we see that Pb is being reduced from +6 to +4, while Cl is being oxidized from +1 to -1. Therefore, the correct balanced equation should show the reduction of Pb and the oxidation of Cl.

The balanced equation for the reaction is:

2Pb(OH)42-(aq) + 6ClO-(aq) → PbO2(s) + 6Cl-(aq) + 2H2O(l) + 4OH-(aq)

In this balanced equation, the number of atoms and charges are equal on both sides, and the correct oxidation states of each element are maintained.

Therefore, your initial attempt to balance the equation was incorrect. You need to account for the proper oxidation states and the number of atoms on both sides of the equation to ensure it is balanced.