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)`.
`2 ZnS + 3 O_(2) rarr 2 ZnO + 2 SO_(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) + 8 O_(2) rarr 8 SO_(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)O rarr underset(("Colourless"))(2Mn^(2+))+5SO_(4)^(2-) + 4H^(+)),(underset(("Yellow"))(2Fe^(3+))+underset((B))(SO_(2))+2H_(2)O rarr underset(("Green"))(2Fe6(2+)) + SO_(4)^(2-) + 4 H^(+)):}`
Thus, solid 'A' = `S_(8)` and gas 'B' = `SO_(2)`.