Selectivity of halogens in halogenation of alkanes.please give me it's answer throughly.

Different halogens give different reactivity during halogenation.

1.The reactivity of the halogens decreases in the following order: F₂> Cl₂> Br₂> I₂.
2.We shall confine our attention to chlorine and bromine, since fluorine is so explosively reactive it is difficult to control, and iodine is generally unreactive.
3.Chlorinations and brominations are normally exothermic.

Chlorine is more reactive and less selective and bromine being more selective is less reactive.