Multiple choice Oxygen and carbon always combine in a 1:2 mass ratio. This is an example of which law? Law of Conservation of Mass Law of Definite Proportions Law of Definite Mass Law of Conservation of Proportions Reveal answer Fill a bubble to check yourself B Correct answer Explanation The Law of Definite Proportions states that a given chemical compound always contains its component elements in a fixed, definite ratio by mass, regardless of the source or method of preparation.