Answer:
The correct answer is B) Fe3O4, also known as magnetite.
Step-by-step explanation:
When mild steel is cut, it reacts with oxygen in the air to form an oxide layer on the surface. This oxide layer, commonly referred to as mill scale, is primarily composed of iron (Fe) oxides. The specific iron oxide that forms during the cutting process of mild steel is Fe3O4, which is magnetite. Magnetite is a black or dark gray compound and is commonly observed as a light gray-colored oxide on the surface of the cut steel.