Question

How many moles of nitrogen are needed to produce 8.2 moles of ammonia by reaction with hydrogen.

Answer 1

$N_2+3H_2\to 2N{H}_3$

2 mole of NH₃ are produced by 1 mole of N₂.
So, 8.2 moles of NH₃ will be produced by (1/2) x 8.2 = 4.1 moles of N₂.