If the reaction H2(g) + Cl(g) <-> has reached equilibrium, what is the effect of doubling the volume of..?

the reaction vessel?
a.) the reaction will shift left to right
b.) the reaction will shift right to left
c.) there will be no effect
d.) what happens depends on the temperature
I thought it was (b), does any one have any opinion on this question, thanks.
4 answers 4