how many moles are there in each one of the following?

(A)19.0 atoms of fluorine.

(B) 280 g of silicon

A)Atomic wt. of F is 19.
No. of moles  = given mass /atomic mass = 19g /19g = 1 mole of F atoms in 19g sample of F.
B) Atomic wt. of Si is 28g.
No. of moles  = given mass /atomic mass = 280 g /28 g = 10 moles of Si atoms in 280g sample.