The correct answer is b) the law of definite proportions.
The law of definite proportions states that in a chemical compound, the elements are always present in fixed, definite proportions by mass. This means that the ratio of the masses of the elements in a compound is constant.
In the given scenario, we observe that in the first reaction, 4.0 grams of oxygen combine with 3.0 grams of carbon to form a compound. In the second reaction, 8.0 grams of oxygen combine with 3.0 grams of carbon to form another compound. The consistent ratio of the masses of oxygen to carbon in both reactions (4:3