# In the reaction NH_4NO_2(s) -> N_2(g) + 2H_2O(g), how many liters of nitrogen gas is produced if 50.0 L of water is produced at STP?

If $50 \cdot L$ of water gas were evolved, then we can immediately see that a $25 \cdot L$ volume of dinitrogen was likewise evolved.
$N {H}_{4} N {O}_{2} \left(s\right) \rightarrow {N}_{2} \left(g\right) + 2 {H}_{2} O \left(g\right)$.
Both products are gaseous. Because $V \propto n$ at constant temperature and pressure, the stoichiometry is easy to assess. Of course if $50 \cdot L$ of ${H}_{2} O \left(l\right)$ were evolved, it would be a different story.