Heptane is always composed of 84.0% carbon and 16.0% hydrogen. this illustrates the law of multiple proportions. conservation of mass. definite proportions. all of the above

Heptane is always composed of 84.0% carbon and 16.0% hydrogen. This illustrates the "law of definite proportions".

Option C

Explanation:

Proust's law states that every chemical compound used to made up of element constituents with constant proportions in terms of its mass and also independent from its sources and synthesis method. In 1779, Joseph Proust gave other names to the Proust's law as, the law of composition or definite proportions or constant compositions.

This can understood from given example like: Oxygen is composed of 8/9 of the mass of any sample of pure water while the hydrogen fills up the remaining 1/9 of the mass. The basis of stoichiometry is structured with the law of multiple proportions along the law of definite proportions.