Which of the following materials practically possesses no elasticity (i.e., shows very little reversible strain), especially in common room-temperature service?

Introduction / Context:
Elasticity refers to reversible deformation. Elastomers like spandex and many rubbers display large recoverable strains. In contrast, highly crosslinked hard materials show minimal elasticity and behave rigidly.

Given Data / Assumptions:

• Vulcanite (ebonite) is heavily crosslinked hard rubber.
• Spandex is a specialty elastomer with extreme stretch and recovery.
• Polysulfide rubber is an elastomer; cured epoxy is rigid but retains a small elastic range before brittle failure.

Concept / Approach:
High crosslink density eliminates the chain mobility necessary for large elastic strains. Ebonite, produced by vulcanising rubber with high sulfur content, is essentially a hard, rigid material exhibiting negligible elastic extension compared to elastomers.

Step-by-Step Solution:
Contrast elastomers (spandex, polysulfide) with hard networks (ebonite, epoxies).Identify the material essentially devoid of practical elasticity.Select vulcanite (ebonite).

Verification / Alternative check:
Property tables list ebonite with high hardness and very low elongation at break, confirming minimal elasticity.

Why Other Options Are Wrong:
Spandex: iconic high-elasticity fibre.Polysulfide rubber: elastomeric.Epoxy: rigid but still exhibits a small elastic modulus region; question asks for “practically no elasticity,” best matching ebonite.Natural rubber: classic elastomer.

Common Pitfalls:
Equating “stiff” with “no elasticity”; even stiff solids have an elastic region, but ebonite’s elastic extensibility is extremely low compared to elastomers.

Final Answer:
Vulcanite (ebonite, hard rubber)