Question

A metal wire is pulled by equal forces at the ends. The stress-strain (x) relationship of the wire is given. Point $B$ of the graph is the elastic limit

Answer 1

(A) For $x<x_1$ hook's law of elasticity is valid and when the stress is removed, wire will regain its original shape again means there is no permanent deformation.
A->2,3
(B) For, $x_1<x<x_2$hook's law is not valid but wire will regain its shape if stress is removed.
B->3
(C) For, $x_2<x<x_3$ a Permanent deformation occurs if the wire crosses $x_2$ and even if stress is removed wire's length will keep on increasing.
C->1
(D) At $x=x_3$ there is already a permanent deformation and wire has reached upto its breaking stress. Now if furthere more stress is applied then wire breaks.
D->1,4