Which discovery by Lavoisier established that sulfur is an element, not a compound?

• A. He drew up the first list of elements
• B. He reformed chemical nomenclature
• C. He discovered that sulfur is an element, not a compound
• D. He proved that matter is neither created nor destroyed when it changes form

Answer: (C)

Understanding what defines an element is the key idea here. Lavoisier helped establish that an element is a substance that cannot be broken down into simpler substances by chemical means. When this framework is applied to sulfur, it supports classifying sulfur as a basic substance in its own right, not a composite of other substances. This is why identifying sulfur as an element, rather than a compound, is the most direct and relevant discovery attributed to Lavoisier in this question.

The other achievements are important in their own right—Lavoisier organized a list of elements, reformed chemical naming, and demonstrated the conservation of mass—but they do not specifically address the elemental nature of sulfur.