The molecular mass of sodium = 23g
One mole of sodium consists of 23 g of sodium
One mole consists of 1 Avagadro(6.022 x 10^23 molecules) number of molecules
Therefore 23 g consists of 6.022 x 10^23 molecules of Sodium.
Hence 7.45 x 10^3 g of Sodium will consist of x no of molecules of sodium.
x no of molecules =
(7.45 x 10^3 g/23 g) x (6.022 x 10^23)
=1950.6 x 10^ 23 molecules (atoms).