A pale yellow substance `(A)` when heated with `conc. HNO_3` evolves a brown coloured gas `(B)`. The substance `(A)` also dissolves in sodium sulphite solution on heating. A clear solution `(c)` is formed which on acidification gives a turbid solution and a pungent smelled gas `(D)` which is formed by the substance `(A)` in air. The solution `(c)` decolourises iodine solution, Identify `(A)` to `(D)`.

Explanation

(i) `2 NH_(4)Cl + K_(2)Cr_(2)O_(7) rarr underset("Amm. dichromate")((NH_(4))_(2)Cr_(2)O_(7)) + 2 KCl`
(ii) `(NH_(4))_(2)Cr_(2)O_(7) overset("Heat")(rarr) underset(("A"))(N_(2)) + Cr_(2)O_(3) + 4 H_(2)O`
(iii) `3 Mg + N_(2) overset(Delta)(rarr) underset("Magnesium nitride")(Mg_(3)N_(2))`
(iv) `underset("Calcium carbide")(CaC_(2))+N_(2) overset("Heat")(rarr) underset("Cal. cyanamide (B)")(CaCN_(2)) + C`
(v) `underset((B))(CaCN_(2))+3H_(2)O rarr underset("Cal. carbonate (C)")(CaCO_(3)) + underset("Ammonia (D)")(2NH_(3))`
(vi) For reaction with Nessler's reagent, refer to Eq. (i), P-5 above.