F2 : Pale yellow gas.
Cl2 : Green gas.
Br2 : Red-Brown liquid.
I2 : Grey solid.
Boiling points increase down the group as the strength of the Van der Waals forces increases as the size and relative mass of the atoms increases. Its shown in the physical state from fluorine to iodine.
Electronegativity decreases down the group. Electronegativity is the ability of an atom to attract the bonding electrons in a covalent bond. The larger halogens attract electrons less than smaller ones, so as the atoms become larger the electronegativity decreases.
The halogens gain an electron when they react and become less reactive down the group as the atoms become larger and less electronegative. They are also less oxidising down the group.
A halogen will displace a halide from solution if the haide is below it in the periodic table.