Composition refers to the pats or compunents of a sample of matter and their relative proportions.Ordinary water is made up of two simpler substances hydrogen and oxygen present in certain fixed proportions.A chemist would say that the composition of water is 11.19% hydrogen and 88.81%oxyen by mass.Hydrogen peroxide a substance used in bleaches and antiseptics is also made up of hydrogen and oxygen but it has a sifferent composition .hydrogen peroxide is 5.98% hydrogen and 94.07% oxygen by mass.