The correct answer is option 2, Keratin. Keratin is a structural protein that is found in the outer layer of our skin, nails, and hair. It is a tough and fibrous protein that provides strength and rigidity to these structures.
Option 1, Histone, is a type of protein that helps DNA organize and compact itself within the nucleus of cells. It is not found in hair.
Option 3, Elastin, is a protein found in connective tissues that allows them to stretch and recoil. It is not present in hair.
Option 4, Actin, is a protein involved in muscle contraction and cell movement. It is not found in hair.
Overall, keratin is the main protein responsible for the strength and structure of hair.