The number of moles of hydrogen molecules required to produce 20...

Haber’s process ${N}_{2}\left(g\right) + 3{H}_{2}\left(g\right) ⇌ 2N{H}_{3}\left(g\right)$

According to the reaction,

2 moles of ammonia are produced from 3 moles of ${H}_{2}$

i.e., 1 mole of ammonia is produced from $\dfrac{3}{2}$ moles of ${H}_{2}$

Thus, 20 moles of ammonia $= \dfrac{3}{2} \times 20 = 30$ moles of ${H}_{2}$

Hence, 30 moles is the correct option.