Answer:
Hydrogen sulfide
Step-by-step explanation:
A nonoxidizing acid is the acid which cannot act as oxidizing agent and thus furnish hydrogen ions. Example: HCl
Iron(II) sulfide reacts with nonoxidizing acid, say hydrochloric acid to give rotten egg smelling gas, H₂S (Hydrogen sulfide).
The reaction is shown below:
FeS (s) + 2HCl (aq) ⇒ FeCl₂ (s) + H₂S (g)
A general reaction is also shown below of the reaction of Iron(II) sulfide with any nonoxidizing acid, HX as:
FeS (s) + 2HX (aq) ⇒ FeX₂ (s) + H₂S (g)