Final answer:
The correct number to balance the equation KClO3 → 2KCl + 3O2 is 2, making the balanced equation 2 KClO3 → 2KCl + 3O2.
Step-by-step explanation:
To balance the chemical equation for the decomposition of potassium chlorate, KClO3, into potassium chloride, KCl, and oxygen, O2, we need to ensure that the number of atoms of each element is the same on both sides of the equation. The equation provided is ___KClO3 → 2KCl + 3O2. By inspecting the equation, we see that we need to have six oxygen atoms on both sides. This means we need to start with two KClO3 molecules, which will decompose into two KCl and three O2 molecules (as each KClO3 molecule contains three oxygen atoms).
Therefore, the coefficient that balances the decomposition reaction of potassium chlorate is 2, making the balanced equation: 2 KClO3 → 2KCl + 3O2.