Law of definite proportion states that the individual elements that constitute a chemical compound are always present in a fixed mass ratio. (a) The ratio of oxygen in H2O and H2O2 with respect to fixed mask of hydrogen atom is a whole number. This is the statement of "law of multiple proportion." (b) As the ratio of elements is fixed, so percentage of oxygen in H2O is constant or fixed irrespective of the source. This statement is with reference to law of definite proportion. Thus, this is the correct option. (c) Avogadro's law states that the "equal volume of all gases at the same temperature and pressure should contain equal number of molecules." (d) "Mass can neither be created nor be destroyed" is the statement of "law of conservation of mass."