Question

How many moles is 2.80 x10^24 atoms of silicon?

Answer 1

 The moles   of silicon  is 4.651  moles

 calculation

The  moles  of  silicon   is calculated using  Avogadro's  constant

that  is  according to Avogadro's  law

                                                   1 mole  = 6.02  x 10^23 atoms

                                                   ?  moles  = 2.80 x 10 ^24  atoms  of silicon

 by  cross multiplication

   =  [ ( 1 mole  x 2.80 x 10^24  atoms)  / ( 6.02 x 10 ^23  atoms)]

      =   4.651  moles

Answer 2

Let x moles of silicon contains 2.8x10^24 atoms. 6.02x10^23 atoms are present in 1 mole of Si. Therefore 2.80x10^24 atoms are present in = 2.8x10^24/6.02x10^23 = 4.65 moles of Si.