the blue complex formed on addition of conc. nh4oh solutin to a cu2+ salt solution has the structure? options :

a-[cu(nh3)4]2+

b-[cu(nh3)2]2+

c-[cu(nh3)3]2+

d-[cu(nh4)2]2+

The correct answer is A
[Cu(NH₃)₄]²⁺

In the reaction of Copper salt and NH₄OH( made up of NH₃ and H₂O), copper(II) hydroxide is formed first, which later reacts with NH₃ to give a blue colored complex as shown in the reactions

CuSO₄(aq) + 2 NH₃ (aq) + 2H₂O(l) Cu(OH)₂ + (NH₄)₂SO₄
Pale blue solu. Pale blue solu.

Cu(OH)₂ + NH₃ [Cu(NH₃)₄]²⁺
Pale blue Dark blue complex