Final answer:
The thin unreinforced layer of resin placed on the mold surface in the hand layup process is called a Gel coat. It enhances the appearance and durability of the final composite part. (option B)
Step-by-step explanation:
The thin unreinforced layer of resin placed on the surface of a mold in the hand layup process is called a Gel coat. It is a protective and decorative layer that enhances the appearance and durability of the final composite part. A gel coat is typically made of a specialized polyester or epoxy resin that is pigmented and designed to be smooth and glossy.
For example, in the case of a polymer-matrix composite, the gel coat is applied to the mold surface first to create a smooth and aesthetic finish on the outermost layer of the composite. It also helps to prevent the formation of air bubbles and enhance the adhesion between the laminate layers and the mold surface.
So, the correct answer is B) Gel coat.