The correct answer is option 3: Keratin.

Collagen, which is a protein found in the skin, provides strength and support, but it does not make the skin impervious to water. Melanin, which gives color to the skin, provides protection against UV radiation but does not directly affect the skin`s water resistance. Chitin is a substance found in the exoskeleton of some animals, such as insects, but it is not present in the human skin.

Keratin, on the other hand, is a protein that is a major component of the outermost layer of the skin, called the epidermis. Keratinocytes, which are skin cells that produce keratin, form a barrier on the surface of the skin that prevents water from penetrating into the deeper layers. This layer of keratinized cells acts as a protective barrier, keeping the skin hydrated and preventing excessive water loss. Thus, keratin plays a crucial role in making the skin layer impervious to water.