(a) Upto point A, Hooke’s law is obeyed because the graph is straight line from O to A.
(b) Point B, from the graph it is clear that the wire returns to its original position after being unloaded upto point A only, hence B is elastic limit.
(c) Elastic region – O to B, Plastic region – B to E
(d) Strain varies as directly proportional to load upto point A and aster A, strain increases by greater amount as compared to first case (i.e., O to A) for a given increase in load. Beyond the elastic limit B, the curve does not retrace Backwards as the wire is unloaded but returns along dotted line CO’. Point O’ corresponds to strain at zero load, which shows there is a permanent strain in the wire.