Final answer:
Stainless steels must contain at least 12% chromium to be defined as such. This chromium content is crucial for the corrosion resistance properties of the material.
Step-by-step explanation:
Stainless steels are defined as iron-based alloys that contain at least 10.5% chromium, which increases their corrosion resistance. However, the specific question asks for the minimum percentage of chromium that defines stainless steel. The correct answer is b. 12%. This minimum chromium content creates a passive film of chromium oxide on the surface, which prevents further surface corrosion and blocks corrosion from spreading into the metal's internal structure. In addition to chromium, stainless steel can also include elements like nickel, molybdenum, and nitrogen to enhance certain properties.