Roasting of sulphides gives the gas X as a by product. This is a colourless gas ith choking

Roasting of sulphides gives the gas X as a by product. This is a colourless gas ith choking smell of burnt sulphur and causes great damage to repiratory organs as a result of acid rain. Its aqueous solution is acidic, acts as reducing agent and its acid has never been isolated. The gas X is :-

choking