46.0g Na
Since 22.4L of anything at STP is one mole, you can use your mole fraction to easily determine the # of moles of Na to produce one mole of H2. In this case, 2 moles of Na yield 1 mole H2, so all you need to do now is convert to grams. (Moles x Molar mass) which is 2 moles Na X 23g . this gives you the answer of 46g of Na.
