Roasting of sulphides give 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 (NEET 2013)

The process in which sulphide ores are heated at a very high temperature with excess oxygen is known as roasting. This process is generally carried out for sulphide minerals. The sulphide is converted to an oxide and sulphur is released as sulphur dioxide. Example of such a reaction is- 2 2 2 2 2Cu S+3O 2Cu O+2SO -> Sulphur dioxide gas has a smell of burnt sulphur and is the main component of acid rain. Therefore, the correct answer is option (b) 2 SO