In oxygen difluoride (${\mathrm{OF}}_2$) and dioxygen difluoride $\left({\mathrm{O}}_2{\mathrm{F}}_2\right)$, the oxygen is assigned an oxidation number of

Oxidation number of oxygen in ${\mathrm{OF}}_2=+2$

Oxidation number of oxygen in ${\mathrm{O}}_2{ \mathrm{F}}_2=+1$

Electronegativity of fluorine is more than that of oxygen atom, so, F gains electron with negative charge In oxygen difluoride (${\mathrm{OF}}_2$) and dioxygen difluoride (${\mathrm{O}}_2{\mathrm{F}}_2$) oxygen transfers electron to fluorine atom