Answer :
[tex]1\ mole\ --\ 6.02*10^{23}atoms\\
3.5\ moles--x\\
x=21.07*10^{23}\ atoms[/tex]
No. of atoms = no.of moles x avagadro's constant
= 3.50 x 6.022*10^23
= 21.077 x 10 ^23
= 3.50 x 6.022*10^23
= 21.077 x 10 ^23