3.011 x 10^23 atoms F in grams

1 mol of anything contains 6.02 x 10^23 of those anythings; therefore, 1 mol of F atoms will contain 6.02 x 10^23 atoms of F. And it will have a mass of 19.0 grams (Look up the atomic mass of F on the periodic table.) So,

3.011 x 10^23 atoms x (1 mol atoms/6.02 x 10^23 atoms) x (19.0 g F atoms/1 mol F atoms) = ? grams F. Note how the units cancel to give grams at the end.

b, c, d are done the same way.