The most electronegative halogen is fluorine which is also the most electronegative element.
Down group 7 melting point and boiling point increase due to Van der Waals forces increasing which require more energy to overcome.
Chlorine is a green gas at room temperature.
Bromine is a brown liquid at room temperature.
Down group 7, oxidising ability decreases.
Down group 7, electronegativity decreases.
Down group 7, 1st ionisation energy decreases because the distance between the nucleus and outer shell increases which means less energy is needed to remove the electron.
All halides react with concentrated sulfuric acid to give a hydrogen halide as a product.
Not all halide ions are strong enough reducing agents that they can reduce sulfuric acid to water.