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

The gas `(X)` is ammonia, `NH_3`.
(a) Aqueous solution of `NH_3` is `NH_4 OH`, which is basic and hence truns red litmus blue.
(b) `CuSO_4 + underset (Excess) (4NH_4 OH) rarr underset ("Tetraamminecopper (II) sulphate")([Cu(NH_3)_4]^(2+) SO_4^(2-)) + 4 H_2 O`
`[Cu(NH_3)_4] SO_4` is deep blue in colour and is soluble in water, hence deep blue coloured solution is formed.
( c) `FeCl_3 + 3NH_4OH rarr underset ("Brownish ppt.") (Fe(OH)_3 darr) + 3 NH_4 Cl`
`Fe(OH)_3+ 3HNO_3 rarr underset ("Solution") (Fe(NO_3)_3) + 3 H_2 O`
On addition of `NH_4OH` to `FeCl_3` solution, brown ppt. of ferric hydroxide, `Fe(OH)_3` is formed. `Fe(OH)_3` dissolves in `HNO_3` due to formation of ferrcnitrate, `Fe(NO_3)_3`.