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(N O_3)_2`