Answer:
+5 in KClO3 to -1 in KCl
Explanation:
The balanced equation is:

<u>In KClO3:</u>
The oxidation state of K = +1
Oxidation state of O = -2
Let the oxidation state of Cl = 'x'
Since the molecule is neutral, the net charge is zero. Therefore,
+1 + x + 3(-2) = 0
x = +5
<u>In KCl:</u>
The oxidation state of K = +1
Let the oxidation state of Cl = 'x'
Since the molecule is neutral, the net charge is zero. Therefore,
+1 + x = 0
x = -1
Therefore, the oxidation state of Cl changes from +5 to -1.