Answer: 197 grams
Step-by-step explanation:
According to avogadro's law, 1 mole of every substance occupies 22.4 L at STP and contains avogadro's number
of particles.
To calculate the moles, we use the equation:

Given mass = 405 g
Molar mass = 78.07 g/mol

1 mole of
contains = 2 moles of fluorine
5.19 mole of
contains =
of fluorine
Mass of flourine =

Thus 197 grams of F are in 405 grams of
.