An aqueous of a gas `(X)` shows the following reactions :
(a) It turns red litmus blue.
(b) When added in excess to a copper sulphate solution, a deep blue coloured solution is obtained.
( c) On addition to `FeCl_3` solution, a brownish precipitate is formed, which is solution in `HNO_3`.
Identify `(X)` and give an explanation for step `(a),(b)` and `( c)`.

Explanation

(i) (a) Since gas (X) turns red litmus blue, it must be basic in nature. The only important gas which is basic in character is ammonia `(NH_(3))`. Thus, (X) may be ammonia. This is supported by the observation that it gives a deep blue colour with copper sulphate solution.
(b) Having identified that the gas (X) is ammonia, the reactions at steps (ii) and (iii) may be explained as follows:
(ii) With copper sulphate solution, it gives a deep blue colour due to the formation of tetrammine copper (II) complex.
`CuSO_(4) + underset(underset((X))("Ammonia"))(4NH_(3)) rarrunderset(underset("(Deep blue colour)")("Tetramminecopper (II) sulphate"))([Cu(NH_(3))_(4)] SO_(4))`
(iii) With ferric chloride solution, (X) gives a brown ppt. of ferric hydroxide which dissolves in dilute nitric acid to form ferric nitrate.
`NH_(3) + H_(2)O rarr NH_(4)^(+) + OH^(-)`
`FeCl_(3) + 3 OH^(-) rarr underset(underset(("Brown ppt."))("Ferric hydroxide"))(Fe(OH)_(3)) + 3 Cl^(-)`