The following salts will produce a gas on reacting with hydrochloric acid except

Carbonates, sulphites and sulphides all release a gas with dilute hydrochloric acid.

CaCO₃ gives carbon dioxide: CaCO₃ + 2HCl → CaCl₂ + H₂O + CO₂. Na₂SO₃ gives sulphur dioxide: Na₂SO₃ + 2HCl → 2NaCl + H₂O + SO₂. FeS gives hydrogen sulphide, which smells like rotten eggs: FeS + 2HCl → FeCl₂ + H₂S.

CuSO₄ is a sulphate. Dilute HCl does not release any gas from it, because the strong acid cannot drive off sulphate as a gas. So it is the exception.