Step 1: Understanding the components.
Chitin is the primary component found in the exoskeletons of crustaceans (such as crabs and lobsters) and the cell walls of fungi. It is a polysaccharide made of N-acetylglucosamine.
Step 2: Analyzing the options.
(A) lignin: Incorrect — Lignin is found in the cell walls of plants, not fungi or crustaceans.
(B) cellulose: Incorrect — Cellulose is a component of plant cell walls, not fungal or crustacean structures.
(C) chitin: Correct — Chitin is indeed the common component in both crustacean exoskeletons and fungal cell walls.
(D) peptidoglycan: Incorrect — Peptidoglycan is found in bacterial cell walls, not in fungi or crustaceans.
Step 3: Conclusion.
The correct answer is (C) chitin.