Define the term ligand. cu2+(aq) reacts with ammonia to form the complex ion
[cu(nh3)4]2+. explain this reaction in terms of an acid-base theory, and outline the bonding in the complex ion formed between cu2+ and nh3.

The answer is ligand: a molecule or ion that can bond to a (central) metal ion (to form a complex);
NH3: Lewis base and Cu2+: Lewis acid (need both for mark);
each NH3/ligand donates an electron pair (to Cu2+); forming coordinate covalent/dative covalent bond; i hope this help you.