According to the law of conservation of mass, the mass of the reactants in a reaction must the mass of the products in a reaction.

Equal.

Explanation:According to the law of conservation of mass- in an isolated system mass can neither be created nor destroyed by any chemical reactions or by any physical transformations.This law was given by Antoine Lavoisier in 1789.According to this law, the mass of the Reactant in a chemical reaction must equal the mass of the Product formed i.e mass of reactant the beginning of any reaction must be equal to the mass of the product formed at the end of the reaction.

Result: mass of the reactant must be equal to the product.

In a dynamic equilibrium, the rates of the forward and reverse reactions remain the same.

Also, the concentrations of the reactants and products (O₂ and O₃) are constant.