How does ammonia react with blue solution having `Cu^(2+)` ions ?

Explanation

When ammonia gas is passed through blue solution containing `Cu^(2+)` ions, ammonium hydroxide formed reacts with `Cu^(2+)` ions to give a soluble complex with deep blue colour.
`Cu^(2+)(aq)+4NH_(4)OH(aq)to underset(("Deep blue solution"))underset("Tetraammine copper (II) ion")( [Cu(NH_(3))_(4)]_((aq))^(2+)+4H_(2)O)`