An amorphous solid“A” burns in air to form a gas “B” which turns lime water milky. The gas is also produced as a by-product during roasting of sulphide ore. This gas decolourises acidified aqueous KMnO4, solution and reduces Fe3+ to Fe2+. Identify the solid “A” and the gas “B”and write the reactions involved.


Since, the by-product of roasting of sulphide ore is SO2 so A is S8,so 'A' = S8: ‘B'= SO2
i S8 + 8O2  8SO2ii Ca(OH)2 + SO2  CaSO3 + H2O(iii) 2MnO4-(Violet) + 5SO2 + 2H2O  5SO42- + 4H+ + 2Mn2+(Colourless)(iv) 2Fe+3 + SO2 + 2H2O  2Fe2- + SO42- + 4H+