The change in enthalpy when the constituent elements of a compound in their standard state i.e. pressure is 1 atm and temperature is 298 K forms one mole of compound in its normal state is known as heat of formation of compound.
The symbol for change in heat of formation is [tex]\Delta H_f[/tex].
Every free element in its standard state has value of [tex]\Delta H_f = 0[/tex].
Thus, from the given options only [tex]F_2(g)[/tex] is present in its standard state so, [tex]\Delta H_f[/tex] for [tex]F_2(g)[/tex] is 0.
Hence, [tex]F_2(g)[/tex] will have [tex]\Delta H_f = 0[/tex].
