Correct Answer: Protein

Solution : The correct option is - protein

Silk is primarily composed of fibroin, a protein based polymer. Chemically, fibroin consists of amino acids, including glycine, alanine, and serine, linked together in a specific sequence. These amino acids form the repeating units of the fibroin protein chain. Additionally, silk fibers often contain a coating of sericin, which is another protein that binds the fibroin strands together and gives silk its characteristic luster. So, chemically, silk is primarily a protein-based fiber composed of fibroin and sericin.