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 acidic solutions hydration protects copper ions.
B. In acidic solution protons co-ordinate with ammonia molecules forming `NH_(4)^(+)` ions and `NH_(3)` molecules are not available.
C. in alkaline solutions insoluble Cu`(OH)_(2)` is precipitated which is soluble in excess of any alkali
D. Copper hydroxide is an amphoteric substances.