Gold sol can be prepared byI. Electric dispersion (Bredig's arc) method II. Hydrolysis of gold salt II. Reduction of gold salt V. Oxidation of gold salt V. PeptisationSelect correct method(s).

I. In Bredig's arc method, an arc is struck between two electrodes of a metal (like Pt, Au, Ag or Cu) in water containing traces of an alkali when the metal passes into colloidal solutions.III. A number of metals such as Ag, Au and Pt have been obtained in colloidal state by reducing aqueous solutions of their salts by formaldehyde, hydrazine etc.2HAuCl4+K2CO3⟶2KAuO2+5CO2 2KAuO2+2HCHO+K2CO3⟶Δ2Au(sol)++ 3HCOOK KHCO3KAuO2 acts as the stabiliser of the red gold sol obtained which is represented as m[Au]×AuO2−(n−x)K+xK+