The following reaction is done at STP:
N₂ (g) + 3 H₂ (g) → 2 NH₃ (g)

If 1.5 liters of nitrogen gas are added to an excess of hydrogen gas, how many liters of NH3 gas will form?
a) 0.75 liters
b) 1.5 liters
c) 3.0 liters
d) 4.5 liters​