Law of Conservation of Mass: This law states that mass cannot be created or destroyed in a chemical reaction; it remains constant. For example, if you bake a cake using certain ingredients, the total mass of the cake will be equal to the sum of the masses of those ingredients.
Law of Definite Proportions: Also known as Proust's Law or the Law of Constant Composition, this law states that a given compound always contains exactly the same proportion (by mass) of its constituent elements. For instance, water (H2O) will always have two hydrogen atoms for every one oxygen atom.
Law of Multiple Proportions: This law states that when two elements form more than one compound together, the different masses of one element that combine with a fixed mass of another element are in ratios expressed by small whole numbers. For example, carbon monoxide (CO) and carbon dioxide (CO2) illustrate this law since their ratio is 1:2.