The metal sodium is obtained by electrolysis of common table salt (sodium chloride, nacl). how much sodium chloride needs to be decomposed to obtain 2500 g of sodium?

Solve first for the number of moles of sodium given that the mass is 2500 g by dividing the given mass by the molar mass of sodium. 
                         moles sodium = 2500 g / 23 g/mol
                               moles sodium = 108.7 moles
Since in every mole of NaCl, there is only one mole of sodium then, we conclude that there are also 108.7 moles of NaCl. Multiplying the number of moles to the molar mass of sodium chloride (58.44), the answer would be 6,352.17 grams.