Q. Aluminium surfaces are often ‘anodized’. This means the deposition of a layer of which of the following oxides?
Answer: aluminium oxide
Notes: Anodizing or anodising in British English, is an electrolytic passivation process used to increase the thickness of the natural oxide layer on the surface of metal parts. The process is called "anodizing" because the part to be treated forms the anode electrode of an electrical circuit. Anodizing increases corrosion and wear resistance. The anodized aluminium layer is grown by passing a direct current through an electrolytic solution, with the aluminium object serving at the anode. The current releases hydrogen at the cathode and oxygen at the surface of the aluminium anode, creating a build up of aluminium oxide layer.