Gold sol can be prepared by

I. Electric dispersion (Bredig's arc) method 
II. Hydrolysis of gold salt 
II. Reduction of gold salt 
V. Oxidation of gold salt 
V. Peptisation

Select 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.

$$\begin{gathered} 2{\mathrm{HAuCl}}_4+{\mathrm{K}}_2{\mathrm{CO}}_3⟶2{\mathrm{KAuO}}_2+5{\mathrm{CO}}_2 \\ 2{\mathrm{KAuO}}_2+2\mathrm{HCHO}+{\mathrm{K}}_2{\mathrm{CO}}_3\stackrel{\mathrm{\Delta }}{⟶}2\mathrm{Au}\left(\mathrm{sol}\right)++ 3\mathrm{HCOOK} {\mathrm{KHCO}}_3 \end{gathered}$$

KAuO₂ acts as the stabiliser of the red gold sol obtained which is represented as $\mathrm{m}\left[\mathrm{Au}\right]\times {\mathrm{AuO}}_2^{-}(\mathrm{n}-\mathrm{x}){\mathrm{K}}^{+}\left[{\mathrm{xK}}^{+}\right]$