Limit of proportionality on force-extension graph

Steps:

• Observe the graph: straight line from origin indicates Hooke's law region where extension is proportional to force.
• Identify deviation: point where line curves, marking end of proportionality.
• Limit is at maximum force for linear behavior, before plastic deformation.
• Select option labeling that point.

Why D is correct:

• D marks the force where the graph ceases to be linear, defining the limit per Hooke's law (F ∝ x up to proportionality limit).

Why the others are wrong:

• A: Indicates initial linear region, not the limit.
• B: Points to origin, irrelevant to limit.
• C: Lies in curved region, beyond proportionality.

Final answer: D