Final answer:
The question regarding the Brinell hardness number relates to determining the hardness of cold-worked steel by measuring the size of an indentation under a specific load, which signifies the material's resistance to deformation.
Step-by-step explanation:
The student's question asks about a cylindrical specimen of cold-worked steel and its Brinell hardness number. The Brinell hardness test is used to determine the hardness of materials by pressing a hard, spherical indenter into the surface. The hardness value is a number determined by the size of the indentation produced under a given load applied for a specific period. The larger the indentation, the softer the material. The options provided (200, 250, 300, 350) correspond to different hardness values which categorize the steel's resistance to indentation and, by extension, its strength and ductility. Higher Brinell hardness numbers indicate a harder material.