In qualitative analysis when H2S is passed

Question:

In qualitative analysis when H2S is passed through an aqueous solution of salt acidified with dil. HCl, a black precipitate is obtained. On boiling the precipitate

with dil. HNO3, it forms a solution of blue colour. Addition of excess of aqueous solution of ammonia to this solution gives _________.

(i) a deep blue precipitate of Cu (OH)2

(ii) a deep blue solution of [Cu (NH3)4]2+

(iii) a deep blue solution of Cu(NO3)2

(iv) a deep blue solution of Cu(OH)2.Cu(NO3)2

Solution:

Option (ii) a deep blue solution of [Cu (NH3)4]2+  is the answer.

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