Roasting of sulphides gives the gas X as a by-product. This is a colourless gas with choking 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
(b) SO2 gas is obtained when any sulphide ore is roasted.
2M2S + 3O2 2M2O + 2SO2
This gas exhibits all the characteristics given in the question.