The number of moles of H₂ that are needed to react with 2.0 moles of N₂ is 6.0 moles
calculation
N₂ +3H₂→ 2NH₃
The moles of H₂ is calculated using the mole ratio
That is from equation above N₂:H₂ is 1 :3
therefore the moles of H₂ = 2.0 moles x (3/1) = 6.0 moles