Equimolar Amounts of the Gases N₂ and H₂ Are Mixed $\rightarrow$

Equimolar amounts of the gases N₂ and H₂ are mixed in a closed container fitted with a piston (allowing the volume of the container to change, thus keeping the pressure constant) . Calculate the ratio of the final volume of the container to the initial volume of the container when the reaction N₂ + 3H₂ $\rightarrow$ 2NH₃ goes to completion.

A) 1
B) 2/3
C) 3/2
D) 1/3
E) none of these