Celluloid, an early moldable plastic widely used for films and small articles, is primarily composed of which chemically modified form of cellulose?

Introduction / Context:
Celluloid was among the first commercial plastics, historically used for photographic film, toys, and combs. Recognizing its composition helps distinguish early thermoplastics from later, safer materials and shows how chemical modification of biopolymers creates new properties.

Given Data / Assumptions:

• All options are cellulose derivatives or related materials.
• Celluloid is often plasticized with camphor.
• We focus on the principal polymeric component.

Concept / Approach:
Cellulose can be esterified to make cellulose nitrate (nitrocellulose) or cellulose acetate. Celluloid specifically refers to nitrocellulose plasticized (commonly with camphor), giving a tough, moldable material. This composition also explains the significant flammability associated with celluloid products.

Step-by-Step Solution:

Verification / Alternative check:
Museum conservation literature and polymer histories describe celluloid degradation (nitrous off-gassing) consistent with nitrocellulose chemistry, confirming the identification.

Why Other Options Are Wrong:

• Cellulose acetate: Used for safety film; different polymer.
• Cellulose acetate butyrate: A later mixed ester with improved weatherability.
• Regenerated cellulose: Produced by viscose/lyocell routes; not celluloid.

Common Pitfalls:
Assuming all early films were cellulose acetate; early motion pictures used celluloid (nitrocellulose), which contributed to fire hazards.

Final Answer:
cellulose nitrate