The ultimate tensile strength of structural mild steel is about

The ultimate tensile strength is a measure of the maximum stress that a material can withstand while being stretched or pulled before necking, which is a point where the specimen's cross-section starts to significantly contract. For structural mild steel, the ultimate tensile strength is typically in the range of:

Option B: 260 N/mm²

So, Option B is the correct answer for the ultimate tensile strength of structural mild steel, which is approximately 260 N/mm².