Which law of chemical combination explains the formation of both carbon monoxide and carbon dioxide from the elements carbon and oxygen?

Introduction / Context:
The laws of chemical combination describe how elements combine to form compounds in fixed quantitative relationships. When the same two elements form more than one compound, specific patterns appear in the mass ratios of the combining elements. The formation of carbon monoxide and carbon dioxide from carbon and oxygen is a classic example used to illustrate one particular law. This question asks you to identify which law of chemical combination explains this situation.

Given Data / Assumptions:

• The elements involved are carbon and oxygen.
• Two different compounds are formed from the same pair of elements, namely carbon monoxide and carbon dioxide.
• Mass ratios of oxygen that combine with a fixed mass of carbon are different for each compound.
• We assume standard textbook statements of the laws of chemical combination.

Concept / Approach:
The law of multiple proportion states that when two elements combine to form more than one compound, the masses of one element that combine with a fixed mass of the other element are in simple whole number ratios. In this example, carbon monoxide and carbon dioxide both contain carbon and oxygen but in different mass ratios. For a fixed mass of carbon, the mass of oxygen in carbon dioxide is approximately twice that in carbon monoxide, giving a simple whole number ratio close to 1:2. This behaviour is exactly what the law of multiple proportion describes, so that is the correct law for this question.

Step-by-Step Solution:
Step 1: Note that carbon monoxide and carbon dioxide are formed from the same two elements. Step 2: Recognise that they have different compositions. Carbon monoxide has the formula CO, while carbon dioxide has the formula CO2. Step 3: For a fixed mass of carbon, compare the mass of oxygen in CO and CO2 and find that the ratio is approximately 1:2. Step 4: Recall that the law of multiple proportion deals with simple whole number ratios in mass when two elements form several compounds. Step 5: Match this pattern to the definition of the law and select the law of multiple proportion.

Verification / Alternative check:
You can cross check by briefly revisiting the other laws. The law of conservation of mass states that total mass is conserved in a chemical reaction, which does not specifically address different compounds from the same elements. The law of definite proportions applies to one compound at a time and says that a compound always contains the same elements in the same proportion by mass. The law of reciprocal proportions involves three elements forming two different compounds in a particular ratio. None of these exactly describe the situation of carbon forming both carbon monoxide and carbon dioxide with oxygen, where simple ratios of mass for a fixed element are compared across compounds. Only the law of multiple proportion matches this description.

Why Other Options Are Wrong:
The law of conservation of mass is a general principle about total mass in a reaction, not about multiple compounds of the same elements.
The law of definite proportions explains fixed composition of a single compound, not the relationship between several compounds formed from the same elements.
The law of reciprocal proportions concerns three elements and the ratios in which they combine, which is not the case here.
The law of constant gaseous volume is not a standard law of chemical combination at this level and does not apply to this example.

Common Pitfalls:
Students often confuse the laws of definite proportions and multiple proportion because both involve mass ratios. A helpful memory tip is that definite proportions focuses on one compound, whereas multiple proportion compares several compounds formed from the same pair of elements. Whenever you see more than one compound mentioned, think of the law of multiple proportion. Careful reading of the problem usually clarifies which law is required.

Final Answer:
The formation of carbon monoxide and carbon dioxide from carbon and oxygen is explained by the law of multiple proportion.