Compounds of halogens are used not only as an insecticide but also used as rocket fuel. Iodine is capable of reacting with sodium thiosulphate to produce sodium tetrathionate. Bleaching powder prepared by treating chlorine with slaked lime. Iodine is manufactured from deep seaweeds especially laminaria variety which contains iodine in the form of alkali iodide (NaI & KI).
All the halogen acids are colorless in nature possessing pungent suffocating smell. They are acidic in the order. HBr and HI can’t be prepared like HCl by using concentrated sulphuric acid because HBr and HI being a strong reducing agent, reduces concentrated sulphuric acid to sulphur dioxide. Hence phosphoric acid [H3PO4] is used instead of concentrated sulphuric acid to prepare HBr and HI. Since phosphoric acid is non–oxidizing agent.