The correct option is B aluminium oxide
Anodizing is one of the methods used for preventing rusting. During anodizing process, dilute acid is taken in an electrolytic cell and aluminium article is dipped in it as anode. On passing an electric current the hydrogen gas is released at cathode and oxygen gas is released at anode. A reaction of aluminium with oxygen occurs at anode and a protective layer of hydrated aluminium oxide is formed on the metal surface.