Which of the following statements indicates that law of multiple proportion is being followed?

At constant temperature and pressure 200 mL of hydrogen will combine with 100 mL oxygen to produce 200 mL of water vapour.

When magnesium burns in oxygen, the amount of magnesium taken for the reaction is equal to the amount of magnesium in magnesium oxide formed.

Sample of carbon dioxide taken from any source will always have carbon and oxygen in the ratio 1 : 2.

Carbon forms two oxides namely $C{O}_2$ and $CO$, where masses of oxygen which combine with fixed mass of carbon are in the simple ratio 2 : 1.