Assertion (A): Silver is a ductile material,
Reason (R): For a ductile material, yield point and breaking point are separated by a larger distance than for brittle materials on the stress- strain curve.
A. Both assertion and reason are true and the reason is the correct explanation of the assertion.
B. Both assertion and reason are true, but reason is not correct explanation of the assertion
C. Assertion is true , but the reason is false
D. Assertion is false, but the reason is true

Hint:Ductile materials can bear significant plastic deformation prior to the breaking point whereas in the case of brittle materials, it can bear very small plastic deformation prior to the breaking point. Ductile material absorbs more energy as compared to the brittle material.

Complete answer:
We know that when an external force or load applied on a material, it deforms plastically (can able to regain its original shape and size) then deforms plastically (permanent change in shape and size).Now we know that the ductile materials are those materials that can bear significant plastic deformation before fracture or breaking. This type of material absorbs a large amount of energy before breaking. Some examples of such materials are aluminium, silver, copper, rubber, etc.

The figure below represents the stress and strain curve of the ductile material:

Brittle materials are those materials that exhibit minor plastic deformation before breaking and they absorb a very small amount of energy before breaking. Example: concrete, glass, cast iron, stone, etc.

The figure below represents the stress and strain curve of the brittle material:

The yield point is the point beyond which the materials start deforming plastically and the breaking point is the point at which the material breaks or fracture takes place.We know that silver is a ductile material. So, the assertion is correct.Ductile material undergoes significant plastic deformation and the distance between the yield point and the fracture point is very large as compared to brittle material.

Hence, the correct option is A.

Note:The ultimate strength of the material is the maximum value of stress that a material bears without undergoing any breakage or fracture. The ultimate strength of the ductile material is more than the brittle material as ductile material absorbs more energy.