What is the oxidation number of F in F (difluorine)?
When we talk about the oxidation state (or oxidation number), it describes the effective charge of some atom in a compound or some element which represents the degree of its possible oxidation (or loss of electrons).
There are some basic rules for determining the oxidation state of some atom or element:
group I elements always have +1 oxidation state when in some compound
group II elements always have +2 oxidation state when in some compound
group 7A elements have -1 oxidation state (in most cases)
oxygen (O) atom always has -2 oxidation state, except in the case of HO or when it is combined with fluorine
hydrogen (H) atom has +1 oxidation state when combined with non-metals, but it has -1 oxidation state when combined with metals or boron (B)
free elements always have oxidation state equal to zero (0)
In our case we have difluorine (F).
We already mentioned that free elements always have oxidation number 0 and in this case we have a molecule which is consisted of two atoms of the same element - fluorine (F). Thus, we can conclude that fluorine (F) has oxidation number 0 in difluorine (F).