Bredig's arc method cannot be used for the preparation of colloidal sol of ? This question has multiple correct options
A. Copper
B. Gold
C. Silver
D. Sodium

Hint :To obtain colloidal sols of metals such as gold, silver, and platinum, the Bredig's arc process is used. Between the electrodes of the metal immersed in the dispersion media, an electric arc forms. The extreme heat evaporates the metal, which subsequently condenses into colloidal-sized particles.

Complete Step By Step Answer:
First of all we will discuss what Bredig's arc method is: Bredig's arc method, also known as electrical disintegration, is a method for making colloidal solutions of metals like gold, silver, and platinum.
Both dispersion and condensation are used in this process. Under the surface of water containing some stabilising agent, such as traces of potassium hydroxide, an arc is struck between electrodes. The arc's tremendous heat vaporises portions of the metal, which subsequently condenses when exposed to cold water. As if it were an ice bath, the water is kept frigid. A little amount of potassium hydroxide is applied to the colloidal particle to stabilise it.
When the dispersion medium is an organic liquid, this approach is not suited since it causes significant charring
Now, coming to the question:
Although Bredig's arc method is used to generate colloidal metal solutions, it is not suited for preparing a colloidal solution of copper and sodium, or when the dispersion medium is an organic liquid, because it requires a lot of stirring.
So, the correct options are: (A) Copper and (D) Sodium.

Note :
Colloidal gold is a sol or colloidal suspension of gold nanoparticles in a fluid, most commonly water. Gold nanoparticles are the topic of extensive research, with a wide range of potential or promised uses in electron microscopy, electronics, nanotechnology, materials science, and healthcare. It will be fascinating to investigate its various features.