Final answer:
Keratin is the protein that provides a water repellant and toughening quality to the skin. Collagen, melanin, and fibroblasts have different functions in the skin.
Step-by-step explanation:
The protein that provides a water repellent and toughening quality to the skin is keratin.
Keratin is a tough, fibrous protein that is found in the skin, hair, and nails. It gives these structures their hard and water-resistant properties.
Collagen is another fibrous protein found in the skin, but it provides tensile strength rather than water repellency. Melanin is a pigment that gives color to the skin, hair, and eyes. Fibroblasts are cells found in connective tissue and are responsible for producing collagen and other components of the extracellular matrix.