When the substance is heated, it produces two distinct products:
1. White smoke
2. A black solid
Analysis:
1. Mixture (Option A): A mixture consists of two or more substances that are physically combined, but not chemically bonded. When heated, components of a mixture might separate or react independently. However, mixtures often do not form entirely new substances upon heating.
2. Element (Option B): An element is a pure substance made of only one type of atom. Most elements do not decompose into two different substances (white smoke and black solid) upon heating. Elements usually change phase (solid, liquid, gas) without producing new substances.
3. Compound (Option C): A compound is a chemical substance composed of two or more elements chemically bonded together. Heating a compound can lead to chemical reactions that produce new compounds or elements. The decomposition of the compound into a white smoke and a black solid suggests that it underwent a chemical reaction.
4. Diotic Molecule (Option D): It's likely there was a typographical error here, and you meant "diatomic molecule" (a molecule composed of two atoms). Common diatomic molecules like O₂, N₂, H₂, etc., typically do not produce both a smoke and a solid when heated.
Thus, the answer is:
[tex] \: \boxed{\text{C. a compound}}[/tex]
