Answer
d. $$N_2 + 3H_2 \longrightarrow 2 NH_3$$
Work Step by Step
This reaction only produces ammonia, so (a) is wrong.
b. is not balanced, there are 2 N atoms on the left and only 1 on the right.
c. "N" is not the correct reactant for this reaction.
d. is correct
e. There is nothing wrong with that equation, but d. is more correct because it has the smallest integer numbers, which is more appropriate.
