Final answer:
The acid mantle protects the cuticle of the hair, which is the outermost layer and serves as a protective barrier.
Step-by-step explanation:
The acid mantle is a protective film of natural oils, sweat, and amino acids that work to protect the surface of the skin and hair. It is important in maintaining the acid balance of the hair and skin, as well as protecting against bacteria and other potential contaminants. The correct answer to the question is that the acid mantle protects the cuticle, which is the outermost layer of the hair shaft. The cuticle serves as the first line of defense against environmental and mechanical damage to the hair.