Group 7 are called halogens and are diatomic molecules to remain stable. As group 7 elements have varying reactivity, with fluorine being the most reactive as it has the highest oxidising ability, they carry out displacement reactions. The oxidising ability of Group 7 halogens decreases down the group.
Halide ions, also Group 7 ions, are reducing agents. With the reaction of sodium halides with sulfuric acid, different halides have different reducing power and produce different products. We can test the presence of different halide ions by using the silver nitrate test.
Chlorine can be used to treat drinking water and water in pools. Although chlorine is considered toxic, its positive effects of water treatment outweight its drawbacks hence it is still being used for water treatment nowadays. Chlorine can also be used to form household bleach, which is also known as sodium chlorate (I).