What are the molar ratios of reactants and products in dinitrogen reduction by dihydrogen?

Well, $\text{dinitrogen : dihydrogen : ammonia = 1 : 3 : 2} .$
${N}_{2} + 3 {H}_{2} \left(g\right) \rightarrow 2 N {H}_{3} \left(g\right)$