All samples of a given compound, regardless of their source or how they were prepared, have the same proportions of their constituent elements. Which law does this refer to?

Law of constant compositions

Explanation:

The law of constant composition is the law that guides this principle. It is one of the laws of chemical combinations. The others being law of multiple proportion, law of reciprocal proportion and law of conservation of matter.

What the law is trying to say regardless of where or when a particular substance is obtained, it contains exactly the same proportions and constituent of elements. This means its identity remains constant regardless