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 `KMnO_(4)` solution and reduces `Fe^(3+)` to `Fe^(2+)` . Identify the solid A and the gas B and write the reactions involved.

Explanation

Since, the by - product of roasing of sulphide ore is `SO_(2)`, so A is `S_(8)` 'A' `=S_(8), 'B' SO_(2)`
Reactions
("i) `S_(8)+8O_(2)overset(Delta)to8SO_(2)`
(ii)`Ca(OH)_(2)+SO_(2)toCaSO_(3)+H_(2)O`
(iii) ` underset(("Violet"))(2MnO_(4)^(-))+5SO_(2)+2H_(2)Oto5SO_(4)^(2-)+4H^(+)underset(("Colourless"))(2Mn^(2+))`
`2Fe^(3+)+SO_(2)+2H_(2)Oto2Fe^(2-)+SO_(4)^(2-)+4H^(+)`