In the law of definite proportions the ratio is of what?

Correct answer: Masses of elements

The direct answer is A: the masses of the elements. The law of definite proportions states that a pure chemical compound always contains the same elements combined in the same fixed ratio by mass, regardless of where the sample came from or how it was prepared. For example, pure water contains hydrogen and oxygen in a fixed mass ratio of 1:8. The ratio concerns the elements forming the compound, not their colours, smells or classroom labels. Option A is correct because it names the measured quantities in this law. Option B is wrong because container colour has no necessary chemical relationship with composition. Option C is wrong because odour is a sensory property, not the fixed quantitative relationship stated by the law. Option D is irrelevant because class numbers are administrative labels and have nothing to do with chemical composition. A useful distinction is that definite proportions concerns one pure compound and its fixed mass composition; it does not say that every mixture has a fixed composition. Memory cue: definite proportion = definite mass ratio of elements in a pure compound.