Which of the following postulates of Dalton's atomic theory explains the law of definite proportion?

The law of definite proportions states that individual elements that constitute a chemical compound are always present in a fixed ratio. The relative number and kind of atoms in a compound remain constant. This explains the law of definite proportion. For example, in carbon dioxide (CO₂​), the ratio of carbon and oxygen will always remain constant, i.e. 1:2, irrespective of where the sample of carbon dioxide is taken from.