When solid S1 is heated, it breaks up into gas G and another solid S2. The solids S1 and S2 and the gas G are all pure substances. On the basis of this information alone, which substance or substances must be compounds? A. S1 only B. S2 only C. S1 and S2 D. S1 and G

A.S1 only

Explanation:

A compound is one of the pure substances (other being element) that forms when two or more atoms of an element are chemically combined. According to this question, a solid S1 is heated and it breaks up into gas G and another solid S2 as follows:

S1 (s) ➡ G (g) + S2 (s)

Based on the information in the questio, the solids S1, S2 and the gas G are all pure substances. However, since solid S1 broke down into two other pure substances, it means solid S1 is originally a chemical combination of both products, which denotes a COMPOUND. Note that Gas G and Solid S2 are most likely elements.