Final answer:
When iron(II) sulfide is treated with a nonoxidizing acid, sulfur dioxide gas is produced. This reaction typically yields a soluble iron(II) salt alongside the SO2 gas release.
Step-by-step explanation:
The gas produced when iron(II) sulfide (FeS) is treated with a nonoxidizing acid is sulfur dioxide gas (SO2). During this reaction, the iron(II) sulfide reacts with the acid to release sulfur dioxide gas and form a soluble iron(II) salt.
This type of reaction is consistent with the behavior of other metal sulfides when they interact with nonoxidizing acids, commonly releasing sulfur dioxide as a byproduct. For example, when iron(II) sulfide is treated with hydrochloric acid (HCl), the reaction produces sulfur dioxide, iron(II) chloride (FeCl2), and water (H2O).