ANS:C - Round specimen of ductile metal.

Cup and cone fracture is a type of fracture commonly observed in ductile materials, especially in materials subjected to tensile loading. It is characterized by the formation of a cup-shaped region at the fracture surface, followed by a conical extension. This fracture pattern indicates significant plastic deformation prior to fracture. Out of the options provided:

• Cast iron: Cast iron is generally brittle and prone to brittle fracture rather than cup and cone fracture.
• Soft brass: While brass is ductile, the term "soft brass" implies a material with reduced strength and hardness, which might exhibit ductile behavior but not necessarily cup and cone fracture.
• Round specimen of ductile metal: This configuration is commonly used in tensile testing, where ductile materials tend to deform uniformly and exhibit cup and cone fracture upon failure.
• Flat tensile specimen of ductile metal: Similar to the round specimen, a flat tensile specimen of a ductile metal subjected to tensile loading would also exhibit cup and cone fracture.