From the law of conservation of mass which states that mass in an isolated system can neither be created nor destroyed in a chemical reaction.
According to the law of conservation of mass, the mass of the products in a chemical reaction must equal the mass of the reactants, that is total mass of the system is unchanged after the chemical reaction.
So therefore, the reaction of
AgNO3(aq) + HCl(aq) --> AgCl(aq) + HNO3(aq)
the mass of the solution before and after the reaction is unchanged.
