How can you justify the the law of conservation in a chemical equation?

Explanation

Chemical equation : A chemical equation is symbolic form of a reaction in which the reactants and products are separated by an arrow mark.
Eg : `Cu+O_(2)rarrCuO`
2) Balanced chemical equation : A chemical equation in which the number of atoms of different elements on the reactants side (left side) are same as those on product side (right side) is called is balanced chemical equation.
Eg : `2Cu+O_(2)rarr 2CuO`
3) Law of conservation of mass : All the chemical equations must balance, because atoms are neither created nor destroyed in chemical reaction.
4) According to the law of conservation of mass, the total mass of the substances that are taking part in a chemical reaction must be the same before and after the reaction.
The number of atoms of each element before and after must be the same in a balanced equation.
Hence, the law of conservation in a balanced equation exists.