Which of the following chemicals is primarily responsible for breaking down the hair's disulfide bonds during a perm?

Ammonium Thioglycolate is primarily responsible for breaking down the hair's disulfide bonds during a perm because it is a reducing agent used in chemical wave processes. When applied to the hair, it penetrates the hair shaft and cleaves the disulfide bonds that give the hair its natural structure and shape. This allows the hair to be reshaped into new forms, such as curls or waves, by wrapping it around rods.

This chemical specifically acts upon the sulfur bonds in the keratin protein of the hair, enabling the stylist to manipulate the hair into the desired curl pattern once the hair is neutralized, allowing it to return to a stable state. Other options mentioned, such as hydrogen peroxide, glycerin, and isopropyl alcohol, do not serve this purpose. Hydrogen peroxide is primarily an oxidizing agent used for color processes, glycerin is a moisturizer, and isopropyl alcohol is often used as a solvent or disinfectant, but none of these are effective in breaking disulfide bonds in hair during a perm.