(a) Anodising is a process of forming a thick oxide layer of aluminium. During anodising, a clean aluminium article is made the anode and is electrolysed with dilute sulphuric acid. The oxygen liberated at the anode reacts with aluminium to produce a thick protective oxide layer on its surface. Also the oxide layer can be dyed easily to give an attractive finish to the aluminium articles.

(b) Aqua regia is a freshly prepared mixture of concentrated hydrochloric acid and concentrated nitric acid in the ratio 3: 1. It is also called royal water. It is highly corrosive and faming liquid. It can dissolve noble metals like gold and platinum.