Final answer:
The nitrogenous polysaccharide in the cuticle of arthropods is chitin, which forms their protective and flexible exoskeleton.
Step-by-step explanation:
The tough, resistant, nitrogenous polysaccharide found in the cuticle of arthropods is known as chitin. Chitin is composed of repeating units of N-acetyl- ß-D-glucosamine, which is a modified sugar. This complex carbohydrate forms the exoskeleton of arthropods, which includes insects and crustaceans. Chitin provides structural support and protection, contributing to the flexibility and toughness of the exoskeleton. Moreover, it is also a significant component of fungal cell walls.