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 `Cu(OH)_(2)` is precipitated which is soluble in excess of alkali.
B. copper hydroxide is amphoteric.
C. in acidic solution hydration protects `Cu^(2+)` ions.
D. in acidic solution protons coordinates with ammonia molecules forming `NH_(4)^(+)` ions and `NH_(3)` molecules are not available.
