The extraction of which of the following metals involves complex formation? 

a) Au    b) Cu    c) Ag
 

Cyanide process :- Their process used for Au, Ag by (Mac-Arthur forrest cyanide
process).

Silver and gold are extracted by a method involving complex formation.
Powdered argentite is reacted with a dilute solution of sodium cyanide in the presence of air. The silver from the ore is dissolved in the cyanide solution forming sodium argentocyanide.

Now metallic zinc is added to the complex salt solution which being more electropositive element than silver, displaces it from the solution.