Roasting of sulphides gives the gas X as a byproduct. This is a colorless gas with a cooking smell of burnt sulphur and causes great damage to respiratory organs as a result of acid rain. Its aqueous solution is acidic, acts as a reducing agent, and its acid has never been isolated. The gas X is:

Roasting of sulphides gives the gas SO2 as a byproduct. This is a colorless gas with a cooking smell of burnt sulphur and causes great damage to respiratory organs as a result of acid rain. Its aqueous solution is acidic, acts as a reducing agent, and its acid has never been isolated.
For example, sulphur dioxide gas is obtained by roasting zinc blende or iron pyrites.
2ZnS + 3O2 → 2ZnO + 2SO2
4FeS2 + 11O2 → 2Fe2O3 + 8SO2
Sulphur dioxide dissolves in water forming sulphurous acid. Hence, it is known as sulphurous anhydride.
H2O + SO2⇌H2SO3
It reduces chlorine to HCl.
SO2 + Cl2 + 2H2O → H2SO4 + 2HCl