How many moles of fluoride are contained in 115.6 l at stp?

Let's assume that the gas is an ideal gas.

1 mole of ideal gas has the volume as 22.4 L at STP (273 K , 1 atm)

The given volume is 115.6 L. 

moles in 22.4 L of gas = 1 mol
moles in 115.6 L of gas = (1 mol x 115.6 L) / 22.4 L

                                      = 5.16 mol

the seeing the electronic configuration we can say that the element is fluorine.

fluorine is the most electronegative element in the periodic table.

but by only seeing the configuration we cannot say about its reactivity because we don't know if its configuration after excitation or by addition of electrons.

but if not then, it is the lightest halogen and exists as a highly toxic pale yellow diatomic gas at standard conditions. as the most electronegative element, it is extremely reactive: almost all other elements, including some noble gases, form compounds with fluorine.