Ammonia forms the complex `[Cu(NH_3)_4]^(2+)` with copper ions in alkaline solution but not in acid solution. The reasons for it is:
A. In alkaline solution insoluble `Cu(OH)_(2)` is precipitated which is soluble in excess of any alkali
B. `Cu(OH)_(2)` is amphoteric
C. In acidic solution hydration protects `Cu^(2+)` ion
D. In acid solution proton coordinates with `NH_(3)` forming `NH_(4)^(+)` ion and `NH_(3)` is not available
