Which of the following elements or elemental chemical compounds is commonly utilized in beauty parlors for the purpose of chemical hair setting?

Hair contains keratin proteins which are held together by disulfide bonds ($\text{S}\text{–}\text{S}$ linkages). Chemical hair perming/setting solutions containing sulfur compounds are applied to break these disulfide bonds, allowing the hair structure to re-align, and are then neutralized to fix the hair into the desired configuration.