The Law of Multiple Proportions states that when two elements form more than one compound, the masses of one element that combine with a fixed mass of the other element are in the ratio of small whole numbers. To identify which pair of compounds demonstrates the law of multiple proportions, let's analyze each option: Option A: CH4,CCl4 This pair does not demonstrate the law of multiple proportions, as the compounds have different elements (hydrogen in CH4 and chlorine in CCl4 ) combining with carbon, without a fixed mass of one element combining with varying masses of the other. Option B:BF3,NH3 This option is also not an example of the law of multiple proportions, as these compounds do not contain the same two elements combining in different ratios; BF3 contains boron and fluorine whereas NH3 contains nitrogen and hydrogen. Option C:CO,CO2 This option correctly represents the law of multiple proportions. Both CO and CO2 consist of carbon and oxygen. In carbon monoxide (CO), one atom of carbon combines with one atom of oxygen, whereas in carbon dioxide (CO2), one atom of carbon combines with two atoms of oxygen. Here, the fixed mass of carbon combines with varying masses of oxygen in a ratio of 1:2 (for the oxygen atoms). Option D: NO2,CO2 Like Option A and B, this choice does not follow the law of multiple proportions because each compound has different elements combining with each other; NO2 has nitrogen and oxygen, while CO2 has carbon and oxygen. The correct answer is therefore Option C : CO,CO2, as these two compounds consist of the same two elements, carbon and oxygen, which combine in different simple numerical ratios, fulfilling the criteria of the law of multiple proportions.