Hydrogen Peroxide Decomposes into Water and Oxygen When Exposed to Heat

Hydrogen peroxide decomposes into water and oxygen when exposed to heat or light.A tightly capped bottle of hydrogen peroxide is placed on a mass scale (a balance) and exposed to light for three weeks.The mass reading on the scale does not change.This is an example of

A) the Law of Conservation of Mass.
B) the Law of Definite Proportions.
C) the Law of Constant Composition.
D) the Law of Multiple Proportions.