To balance this equation, the coefficient of KNO3 should be changed to 2 and the coefficient of O2 should be changed to 2. This is because when a chemical equation is balanced, the same number of atoms of each element should be on the reactant side of the equation as on the product side of the equation.
This chemical reaction demonstrates the conservation of mass because the total mass of the reactants (2KNO3 molecules) is equal to the total mass of the products (1KNO2 molecule and 2O2 molecules). Consequently, no mass is gained or lost in the overall reaction.