Molar mass of sodium $=23 \,g$

$1$ mole atom $=6.022 \times 10^{23}$ atoms

$23 \,g$ sodium contains $=6.022 \times 10^{23}$ atoms

$1 \,g$ sodium contains $=6.022 \times 10^{23}$ atoms

$100\, g$ sodium contains $=6.022 \times 10^{23}$ atoms

                     $=2.618 \times 10^{24}$ atoms

By the above method or by formula we find number of atoms in $100\, g$

$Fe$ ;

Number of atoms of an element in a given mass

$=\frac {\rm {Given \,mass}}{\rm {Gram \,atomic\, mass \,100\,g}}$ $\times $ Avogadro's number

$=\frac{{100\,g}}{{56\,g}} \times \,6.022 \times {10^{23}}$

$ = \,1.075\, \times \,{10^{24}}$ atoms

Hence, $100\, g$ of sodium has more number of atoms as compared to $100\, g$ of iron.