Molar mass is 28+32 = 60
So take 3.4 x 10^-7/60 and get about 5.7 x 10^-9
18.99g/mol F = 1 mole of F
1 mole is equal to Avogadro's number which is:
Therefore, one mole of fluorine has 6.02214076 × 10^23 fluorine atoms.
The formula for iron (II) sulfate hexahydrate
FeH12O10S