The term formula units means molecules.
Then, what you are looking for is the mass in 4.5910^24 molecules.
The procedure involves to convert the 4.59 10^24 molecules into moles and use the molar mass of the sodium chloride.
1) Number of moles = 4.59 10^24 molecules / (6.02 10^23 molecules/mol) = 7.62 mol
2) Molar mass of NaCl = 22.99 g/mol + 35.45 g/mol = 58.44 g/mol
3) mass of NaCl = molar mass number of moles = 58.44 g/mol 7.62 mol = 445.31 g of NaCl
Answer: 445.31 g of NaCl.
