An amorphous soild 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 sulohide ore. This gas decolourises acidified aqueous `KMnO_(4)` solution and reduces `Fe^(3+)` to `Fe^(2+)` . Identify the solid A and the gas B and write the reactions involved.

Explanation

(i) Since gas 'B' is obtained as a by -product during roasting of sulphide, therefore, gas 'B' must be `SO_(2)`.
`2ZnS+3O_(2)to2ZnO+2SO_(2)(B)`
(ii) Since gas 'B' is obtained when amorphous solid 'A' burns in air, therefore, amorphous solid 'A' must be sulphur, `S_(8)`.
`S_(8)(A)+8O_()to8S_(2)(B)`
(iii) Gas 'B' reduces acidified `KMnO_(4)` solution and reduces `Fe^(3+)" to "Fe^(2+)` salts as shown below :
`{:underset("Purple")(2MnO_(4)^(-))+underset((B))5SO_(2)+2H_(2)Otounderset("Colourless")(2Mn^(2+))+5SO_(4)^(2-)+4H^(+):}`
`{:underset(("Yellow"))(2Fe^(3+))+underset((B))SO_(2)+2H_(2)Otounderset(("Green"))(2Fe^(2+))+SO_(4)^(2-)+4H^(+):}`
Thus, solid 'A' = `S_(8)` and gas 'B' = `SO_(2)`.