Stoichiometry: efficiency
Yes, that is completely correct. Let me summarize the approach.

If you look at the chemical reaction:
$$\ce{N2 + 3H2 \rightarrow 2 NH3}$$

You can see that you can, at best, make 2 mole of $\ce{NH3}$ per mole of $\ce{N2}$ (for the case here where $\ce{H2}$ is abundant). Given that you have $4.46\; moles$ of $\ce{N2}$ you could at best make $8.92\; moles$ of $\ce{NH3}$ which would be $151.9\; g$. Since you have made only $36.5\;g$ that means that your efficiency is $36.5/151.9=24\%$