Number of atoms in one mole of substance = Avagadro's Number = 6.022 x 10^23.
Number of moles of a substance = Gram molecular/atomic weight divided by molar mass.
Number of moles in 100 gm of Sodium = 100/23 = 4.35.
Number of moles in 100 gm of Iron = 100/56 = 1.79.
Since number of moles of sodium is greater in 100gm, hence sodium has more number of atoms.
option A is correct