Final answer:
The law of definite composition, attributed to Joseph Proust, dictates that a chemical compound always contains the same proportion of elements by mass. The law of multiple proportions, proposed by John Dalton, states that elements can combine in different whole number ratios to form distinct compounds. These laws were foundational in developing the modern scientific understanding of chemical compounds.
Step-by-step explanation:
The law of definite composition and the law of multiple proportions are fundamental concepts in chemistry that emerged from the early scientific understanding of atomic theory. The law of definite composition, also known as the law of constant composition, was proposed by the French scientist Joseph Proust. It states that a given chemical compound always contains exactly the same proportion of elements by mass. For example, water (H₂O) will always have 11.19% hydrogen and 88.81% oxygen by mass, regardless of its source.
On the other hand, the law of multiple proportions was introduced by English chemist John Dalton, which indicates that when two elements form more than one compound, the masses of one element that combine with a fixed mass of the other are in the ratio of small whole numbers. This law supports Dalton's atomic theory by asserting that atoms combine in simple whole number ratios to form compounds.