The above stress-strain diagram is for

Explanation:

Stress-strain diagram:

Yield point:

• The yield point is the point in the stress-strain curve from which transitions from elastic behaviour (where removing the applied load will return the material to its original shape) to plastic behaviour (where deformation is permanent) takes place.  After the yield point material shows permanent deformation on loading.

Plastic deformation:

• As we know plastic deformation is significant in ductile material only, brittle material failed after elastic deformation rather than being deformed permanently. Hence we can observe the yield point on the stress-strain curve for ductile material only. 
• Cast iron and glass are brittle materials, so they do not produce yield point, they just break when stress exceeds a certain limit. Hence we cannot observe any definite yield point in cast iron or brittle materials.

Thus, option(2) is the Correct Answer.