How does Dalton’s atomic theory explain each of the following facts?

(a) A sample of pure NaCl (table salt) obtained from a mine in the United States contains sodium and chlorine in the same ratio as NaCl obtained from a mine in France.

(b) The mass of the hydrogen peroxide molecule, H₂O₂, equals the sum of the masses of the hydrogen, H₂, and oxygen, O₂, molecules from which it is formed.