The cortex of the hair is made up of millions of polypeptide chains cross-linked by three types of side bonds that are responsible for the elasticity and strength of the hair. These bonds are

• A. Hydrogen bonds
• B. Ionic bonds
• C. Disulfide, Salt, and Hydrogen
• D. Salt bonds

Answer: (C)

The bonds that cross-link the hair’s cortex to give it elasticity and strength are disulfide bonds, salt bonds, and hydrogen bonds. Disulfide bonds are covalent links between sulfur atoms in cysteine amino acids; they are the strongest of the three and largely determine the hair’s shape and structural integrity. Salt bonds are ionic connections between oppositely charged side chains; they’re weaker than disulfide bonds and easily affected by pH changes, contributing to how the hair holds a chemical service’s result. Hydrogen bonds are weaker interactions between hydrogen and electronegative atoms, but there are many of them, so they collectively influence how the hair behaves with moisture and heat, affecting temporary elasticity and shape.

Because all three types form the network that gives the cortex its strength and elasticity, this option is the most complete description. Choices mentioning only one or two types don’t capture the full cross-linking system.