In qualitative analysis when `H_2S` is passed through an aqueous solution of salt acidified with dil. HCl, a black precipitate is obtained. On boiling the precipitate with dil. `HNO_3`, it forms a solution of blue colour. Addition of excess of aqueous solution of ammonia to this solution gives .............

Options

A. Deep blue precipitate of `Cu(OH)_2`
B. Deep blue solution of `[Cu(NH_3)_4]^(2+)`
C. Deep blue solution of `Cu(NO_3)_2`
D. Deep blue solution of `Cu(OH)_2 .Cu(NO_3)_2`

Answer

B

Explanation

`H_(2)S_(g) + Cu_(aq)^(2+) to CuS + 2H_(aq)^(+)`
`underset("dilute")(Cus + 10HNO_(3))to underset("Blue")(Cu(NO_(3))_(2) + 8NO_(2) + 4H_(2)O + H_(2)SO_(4) to NH_(3)(aq) [Cu(NH_(3))_(4)]^(2+)` (Deep blue colour)