To solve this problem, we need to understand the composition of the exoskeleton in arthropods.$\newline$Arthropods, such as insects, crustaceans, and arachnids, have an exoskeleton that provides structural support and protection.$\newline$The exoskeleton is primarily composed of a substance called chitin.$\newline$Chitin is a long-chain polymer of $N$-acetylglucosamine, which is a derivative of glucose.$\newline$It is a tough, flexible, and biodegradable material, making it ideal for the exoskeleton.$\newline$Let's analyze the options:$\newline$• Option 1: Cutin - This is a waxy substance found in the cuticle of plants, not in arthropods.$\newline$• Option 2: Cellulose - This is a polysaccharide found in the cell walls of plants, not in arthropods.$\newline$• Option 3: Chitin - This is the correct component of the exoskeleton in arthropods.$\newline$• Option 4: Glucosamine - While it is a component of chitin, it is not the primary substance of the exoskeleton.$\newline$Therefore, the correct option is Option 3: Chitin.