According to the Dalton's atomic theory : The relative number and kinds of atoms are constant in a given compound. Explain that statement ?

The relative number and kinds of atoms are constant in a given compound. This postulate of Dalton’s atomic theory explains the Law of definite proportions.

The law of definite proportion, sometimes called Proust'slaw or the law of definite composition, or law of constant composition states that a given chemical compound always contains its component elements in fixed ratio (by mass) and does not depend on its source and method of preparation.