A white substance (A) reacts with dilute `H_(2)SO_(4)` to produce a colourless suffocating gas (B) and a colourless solution (C )/ The reaction of gas (B) with potassium iodate and starch solution produce a blue colour solution. Aqueous Solution of (A) gives a white precipitate with `BaCl_(2)` solution which is soluble in dilute `HCl`. Addition of aqueous `NH_(3)` or `NaOH` to (C ) produced first a precipitate which dissolves in excess of the respective reagent to poduced a clear solution. Similarly addition of excess of potassium ferrocyanide to (C ) produced a precipitate (D) which also dissolves in aqeous `NaOH` giving a clear solution. Identify (A),(B),(C ) and (D ). Write the equation of the reactions involved.

Answer

`ZnSO_(3)+H_(2)SO_(4) to ZnSO_(4)+SO_(2)downarrow+H_(2)O`
(A) ,(C) ,(B)
`5 SO_(2)+2IO_(3)^(-)+4H_(2)O to I_(2)+5SO_(4)^(2-)+8H^(+)`
`I_(2)`+Starch solution to blue colour solution.
`SO_(3)^(-)+2H^(+) to Ba^(2+)+SO_(2)+H_(2)O`
`Zn^(2+)+2OH^(-) to Zn(OH)_(2)downarrow("white")`
`Zn(OH)_(2)+2OH^(-) to [Zn(OH)_(4)]^(2-)`
`Zn^(2+)+2NH_(3)+2H_(2) to Zn(OH)_(2) downarrow+2NH_(4)^(+)`
`Zn(OH)_(2)downarrow+4NH_(3) to [Zn(NH_(3))_(4)]^(2+)+2OH^(-)`
`3Zn^(+)+2K^(+)+2[Fe(CN)_(6)^(4-) to K_(2)Zn_(3)[Fe(CN)_(6)]_(2)downarrow`
`K_(2)Zn_(3)[Fe(CN)_(6)]_(2)+12OH^(-) to 2[Fe(CN)_(6)]^(4-)+3[Zn(OH)_(4)]^(2-)+2K^(+).`