(i) An aqueous solution of a compound (A) is acidic towards litmus and (A) sublimes at about `300^(@)C`.
(ii) (A) on treatment with an excess of `NH_(4)SCN` gives a red coloured compound (B) and on treatment with a solution of `K_(4)[Fe(CN)_(6)]` gives a blue coloured compound (C).
(iii) (A) on heating with excess of `K_(2)Cr_(2)O_(7)` in the presence of concentrated `H_(2)SO_(4)` evolves deep red vapours of (D).
(iv) On passing the vapour of (D) into a solution of NaOH and then adding the solution of acetic acid and lead acetate, a yellow precipitate of compound (E) is obtained.
Identify (A) to (E) and give chemical equations for the reactions.

Explanation

Since (A) with an excess of `NH_(4)SCN` gives a red coloured compound (B) onan on treatment with `K_(4)[Fe(CN)_(6)]` solution giveas a blue coloured compound, this means that the compound (A) contains `Fe^(3+)` ions ( may be `FeCl_(3)`). The reactions taking place in different steps are as follows :
(i) `underset((A))(FeCl_(3))+ underset("Amm. thiocyanate")(3NH_(4)SCN) to underset("(Red coloured)")underset("(B) Ferric thiocyanate")(Fe(SCN)_(3))+3NH_(4)Cl`
(ii) `underset((A))(4FeCl_(3))+ underset("Pot. ferrocyanide")(3K_(4)[Fe(CN)_(6)]) to underset("(Blue colured)")underset("(C) Ferric ferrocyanide")(Fe_(4)[Fe(CN)_(6)]_(3))+12KCl`
(iii) `underset((A))(2FeCl_(3))+ K_(2)Cr_(2)O_(7)+3H_(2)SO_(4) overset(Heat)to underset("(D) (Red vapours)")underset("Chromyl chloride")(2CrO_(2)Cl_(2))+Fe_(2)(SO_(4))_(3)+2KCl+3H_(2)O`
(iv) `CrO_(2)Cl_(2)+4NaOH to underset("Sod. chromate")(Na_(2)CrO_(4))+2NaCl+2H_(2)O`
`Na_(2)CrO_(4)+(CH_(3)COO)_(2)Pb to underset("(E) (Yellow ppt.)")underset("Lead chromate")(PbCrO_(4))+2CH_(3)COONa`