Answer
The amount of fluorine that form is $28.51 grams$
Work Step by Step
Since the mass ratio of sodium to fluoride is $1.21:1$, meaning 1.21 times more sodium is formed than fluorine, we can solve for the amount of fluorine formed by dividing the amount of sodium formed (i.e. 34.5 grams) by 1.21 to get $28.51 grams$.