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What does the law of definite proportions state
The law of definite proportion states that a given chemical compound always contains its component elements in fixed ratio and independent of its source and method of preparation.
why is the law of definite proportions important
Along with the law of multiple proportions, the law of definite proportions forms the basis of stoichiometry.

Question: who discovered the law
Self-contained rewrite: who discovered the law of definite proportions