Compared to hydrogen and salt bonds, disulfide bonds are:

• A. Weaker
• B. Stronger
• C. More plentiful
• D. Less stable

Answer: (B)

Disulfide bonds are covalent cross-links between cysteine residues in keratin, making them much stronger and more permanent than the non-covalent hydrogen bonds and salt (ionic) bonds that also help hold hair together. Hydrogen bonds are numerous but individually weak, easily broken by water, heat, or humidity. Salt bonds are stronger than hydrogen bonds but are still sensitive to pH changes and environmental conditions. Because disulfide bonds form covalent links, they resist breakage under ordinary conditions and require chemical reducing agents or substantial energy input to break and reform, which is why chemical processing can permanently alter hair structure. So, compared with hydrogen and salt bonds, disulfide bonds are stronger.