The correct answer is option 2, the Law of multiple proportions. This law states that when two elements combine to form more than one compound, the different masses of one element that combine with a fixed mass of the other element are in a simple ratio.

In the case of carbon monoxide (CO) and carbon dioxide (CO2) formation from carbon (C) and oxygen (O), the Law of multiple proportions is applicable. Carbon and oxygen can combine to form two different compounds, CO and CO2. The ratio of carbon to oxygen in these compounds is different. In carbon monoxide, the ratio is 1:1, while in carbon dioxide, the ratio is 1:2. This demonstrates the Law of multiple proportions, as the masses of carbon that combine with a fixed mass of oxygen are in a simple ratio of 1:2.

The other options are not relevant to the formation of carbon monoxide and carbon dioxide. The Law of conservation of mass (option 1) states that mass is conserved in chemical reactions. The Law of reciprocal proportions (option 3) refers to the ratios of different elements combining with a fixed mass of an element. The Law of definite proportions (option 4) states that a compound always contains the same