Correct Option (B)
Anodizing is an electrolytic passivation process used to increase the thickness of the natural oxide layer on the surface of metal parts. For aluminium, this process involves immersing the aluminium object in an acidic electrolyte and passing an electric current through it. The aluminium acts as the anode, and oxygen ions released from the electrolyte react with the aluminium surface to form a dense, protective layer of aluminium oxide (Al₂O₃). This layer enhances corrosion resistance, wear resistance, and provides a porous surface suitable for dyeing.
Incorrect Options:
Chromium oxide (A) is a ceramic material known for its hardness and corrosion resistance, often used in pigments or as a protective coating, but it is not formed during the anodization of aluminium. Anodization specifically refers to the formation of the native metal's oxide.
Nickel oxide (C) is a chemical compound of nickel and oxygen. It has various applications, including in ceramics, batteries, and catalysts, but it is not the product of anodizing an aluminium surface.
Zinc oxide (D) is an inorganic compound used as an additive in numerous materials and products, such as rubber, plastics, ceramics, glass, cement, lubricants, paints, ointments, adhesives, sealants, pigments, foods, batteries, ferrites, fire retardants, and first-aid tapes. It is not formed during the anodization of aluminium.