In this question, we have a stoichiometry question, and the first thing we need to do is to set up the properly balanced equation:
2 Na + 2 H2O -> 2 NaOH + H2
As we can see, the molar ratio of NaOH and Na is 2:2, so we are going to need the same number of moles of Na to produce the same number of moles of NaOH, now we need to find how many moles of NaOH we have in 50 grams, we are going to use its molar mass = 40g/mol
40g = 1 mol
50g = x moles
x = 1.25 moles of NaOH
So if we have 1.25 moles of NaOH, we are also going to have 1.25 moles of Na as a reactant, and using the molar mass of Na = 23g/mol, we can find the final mass:
23g = 1 mol
x grams = 1.25 moles
x = 28.75 grams of Na are required to produce 50 grams of NaOH