How many fluorine atoms are found in 1.92 grams of asf3?

First you need to find out how many moles of AsF3 are in 1.92 grams.  
The molar mass of AsF3 is 131.918 g/mole so  
1.92 g * (1 mole)/(131.918g) = .0146 moles AsF3 

 Each mole of AsF3 has 6.02 x10^23 molecules of AsF3 and each molecule of AsF3 has 3 flourines, so you need to convert from moles to molecules AsF3 to atoms of F 
 0.146 moles AsF3 * (6.02 x 10^23 molecules AsF3)/(1 mole AsF3) * (3 atoms F)/(1 molecule AsF3) = 2.64 x 10^22 atoms F