When iron (II) sulfide was dissolved in excess of hydrochloric acid, 5.6 L of gas was released. The mass of iron (II) sulfide is equal to

Reaction equation:
FeS + 2HCl = H2S ↑ + FeCl2
As can be seen from the reaction equation, the gaseous reaction product is hydrogen sulfide. We calculate the amount of its substance:
n (H2S) = V (H2S) / Vm = 5.6 / 22.4 = 0.25 mol
In the reaction equation, both FeS and H2S have the same coefficients equal to unity. This means that the number of moles of these substances is equal:
n (FeS) = n (H2S) = 0.25 mol.
Hence:
m (FeS) = M (FeS) ⋅ n (FeS) = 88 ⋅ 0.25 = 22 g.