If matter was not composed of atoms, the law definite proportions and law of multiple proportions will not hold true because compound would have random composition.
The law of definite proportions states that all pure samples of a compound contains the same element in a fixed mass ratio.
The law of multiple proportions states that if an element combines with another element to form more than one compound, the mass of the element combines with a fixed mass of the other element in whole number multiples ratios.
Assuming matter was not composed of atoms, the law definite proportions and law of multiple proportions will not hold true because, their will be no definite ratio or composition in compounds.
The law definite proportions and law of multiple proportions are required for the atomic theory as they help prove that matter consists of definite unique particles called atoms.
In conclusion, the existence of atoms is proved true by the law definite proportions and law of multiple proportions.
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