When ammonia is added to a cupric salt solution, the deep blue colour is observed it is due to the formation of 

• A

  ${\left[ {Cu{{\left( {OH} \right)}_4}} \right]^{2 - }}$

• B

  ${\left[ {Cu{{\left( {N{H_3}} \right)}_4}} \right]^{2 + }}$

• C

  ${\left[ {Cu{{\left( {{H_2}O} \right)}_2}{{\left( {N{H_3}} \right)}_2}} \right]^{2 + }}$

• D

  ${\left[ {Cu{{\left( {{H_2}O} \right)}_4}} \right]^{2 + }}$