Answer :

marmal
[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