When a chemical reaction takes place, the number of atoms each element in the reactants the number of atoms of each element in the products

is equal to

Explanation: According to law of conservation of mass, the mass can neither be created nor be destroyed. Thus the mass of products must be equal to the mass of reactants.

In order to have same mass on both sides of the chemical equation, the number of atoms of each element must be same in reactants as well as products.