Limit of proportionality on load-extension graph

Steps:

• Recall that the limit of proportionality is where the load-extension relationship remains linear, following Hooke's law.
• Examine the graph for the straight-line portion, which indicates proportional extension.
• Identify the point where the line deviates from straight, marking the end of proportionality.
• Select the option at that deviation point.

Why A is correct:

• Point A marks the end of the straight-line region, where stress is proportional to strain per Hooke's law (F = kx).

Why the others are wrong:

• B is within the linear region, before proportionality ends.
• C is in the elastic limit or beyond, after non-linearity begins.
• D is in the plastic deformation phase, far past proportionality.

Final answer: A