Bredig's arc method cannot be used to prepare colloidal solution of which of the following

Bredig's arc method is suitable for the preparation of colloidal solution of metal like gold, silver, platinum, etc. An arc is struck between the metal electrodes under the surface of water containing some stabilizing agent such as a trace of KOH. However, Fe does not react with alkalies that is why it is not obtained by Bredig's arc method.