Indium is a silvery white metal with a slight blue color, melting point 156.6 1℃, boiling point of 2080℃ and density of 7.3g/cm3 (20℃). Chemical formula: Between normal temperature and melting point, indium reacts slowly with oxygen in the air, forming an extremely thin oxide film on the surface. At higher temperature, indium reacts with oxygen, halogen, sulfur, selenium, tellurium and phosphorus. Bulk indium does not react with boiling water and alkali, while powdered indium can react with water to produce indium hydroxide. Indium reacts slowly with cold dilute acid and is easily soluble in concentrated hot inorganic acid, acetic acid and oxalic acid. Indium can alloy with many metals. The oxidation states of indium are+1 and +3. The main compounds are in _ 2O _ 3 and in (OH) _ 3, which can form monohalide and trihalide when combined with halogen.