The molecular weight of sodium is 23gr/mol. There is 31.5g sodium react used for reaction. From the equation, you can conclude that for every 2 sodium atoms, there will be 1 H2 gas formed.
The number of the H2 gas molecule formed would be: (2/1) * 31.5g/(23g/mol) = 2.74 mol
In STP an ideal gas will have volume 22.4l/mol. The volume of H2 gas would be: 22.4 l/mol * 2.74 mol= 61.36 liters.
