If 6 liters of hydrogen gas are used how many liters of nitrogen gas will be needed for the above reaction at STP?

For the reaction N₂ + 3H₂ → 2NH₃, the mole ratio of hydrogen gas to nitrogen gas is 3:1. Since 6 liters of hydrogen gas is used, you would need 2 liters of nitrogen gas at STP for this reaction according to the stoichiometry of the reaction.