Step-by-step explanation:
According to the law of conservation of mass, mass can neither be created nor it can be destroyed. It can only be transformed from one form to another.
For example,

Therefore, mass of reactants is as follows.
Mass of Na = 23 g/mol
Mass of Cl = 35 g/mol
Total mass of the reactants is (2 \times 23 g/mol) + (35 g/mol \times 2) = (46 + 70)g/mol = 116 g/mol
Mass of products is as follows.
2NaCl = 2 times (23 + 35) g/mol = 116 g/mol
Thus, we can conclude that the total mass of the chemicals involved in the reaction as the reaction proceeds gets transformed into other form, that is, into the products.