What is the oxidation state of chlorine in KClO3?

##+5##

Excellent question! I love oxidation state questions.

First, let's look at the ##"K"## (potassium). In an ionic compound, the potassium's oxidation state is always ##+1##.

Next, let's look at the chlorate , ##"ClO"_3^-##. The charge on the polyatomic ion is ##-1##. You may be asking yourself, how do I know its charge will be ##-1##?

Since the entire compound ##"KClO"_3## has a charge of ##0## and the ##"K"## will have a charge of ##+1##, the ##"ClO"_3## must balance the ##"K"##'s ##+1## in the form of ##-1## for a net charge of ##0##.

When oxygen is with another element that is less electronegative than it is, the charge on the oxygen is ##-2##. There are ##3## oxygen atoms in the chlorate ion, for a total of ##-6## charge on the total of the ##3## oxygen atoms.

Thus, ##"charge of Cl"## ##+(-6)=-1##. That means that the charge on chlorine in potassium chlorate is ##+5##.

Have a great day!!