You can first start off by solving to see how many moles 50L of N2 gas corresponds to.
You can do this by using the equation:
PV=nRT
Plug in everything you are given, standard temperature and pressure and use the correct R constant for the corresponding units:
1atm standard pressure
273K standard temperature
50L given in problem
0.0821L*atm/mol*K
1*50 = n(0.0821)273
n= 50/ 22.4133
n= 2.2308 mol
Now using the balanced equation:
If: 2NaN3 ==> 3N2
X NaN3 ==> 2.2308 N2
Cross multiply divide and solve for x and you get:
3X= 2*2.2308
X= 1.487 mol NaN3
Now how many grams is this?
Use the atomic weight for NaN3 to find out:
Atomic weight NaN3: 65g/mol
Now get grams:
1.487 mol*65g/mol, moles cancel top to bottom and you have: 96.7g of NaN3