Chitin, the primary structural component of insect exoskeletons, is composed of:

✅ Explanation: Chitin is a nitrogenous polysaccharide and is the primary structural component of an insect's exoskeleton. It is composed of long chains of N-acetylglucosamine, a derivative of glucose, which provides rigidity and strength to the exoskeleton. Chitin is a key component in arthropod exoskeletons, providing both flexibility and strength.

📌Other Options Explanations:
(a) Structural protein: Chitin itself is not a protein, but it often works in conjunction with proteins (like sclerotin) in the process of sclerotization, where the exoskeleton hardens and darkens.
(c) Polyphenols: These are involved in the process of sclerotization but are not the primary component of chitin.

🛑 Additional Information::
Chitin is probably the second most abundant polysaccharide, next to cellulose, in nature.
It is a crucial part of the cell walls in fungi, which make up arthropod exoskeletons.
It is a linear homopolysaccharide composed of N-acetylglucosamine residues in linkage. 
The only chemical difference from cellulose is the replacement of the hydroxyl group at C-2 with an acetylated amino group.