The basic rule of balancing the equation of a chemical reaction is to obtain same number of atoms of each element on both sides of the equation. In other words, a balanced chemical equation contains the same number of atoms of an element on both the reactant side and the product side. In this case, potassium chlorate is the reactant and potassium chloride and oxygen are the products. Potassium chlorate has a chemical formula of KClO3, while potassium chloride is represented by KCl and oxygen by O2.
The balanced chemical equation is given as:
KClO3 --> KCl + 3/2 O2
We can check if the equation is balanced or not, by counting the atoms of each element on both sides of equation. For example, the number of potassium atoms is 1 on both the reactant and product side of equation.
Hope this helps.