What would be the final pressure of $O_2$ in following experiment ? A collapsed polyethylene bag of 30 litre capacity is partially blown up by the addition of 10 litre of $N_2$ at 0.965 atm at 298K . Subsequently enough $O_2$ is pumped into bag so that at 298K and external pressure of 0.990 atm, the bag contains full 30 litre.

Question

$(a)\;6.68 atm\qquad(b)\;0.5 atm\qquad(c)\;0.8 atm\qquad(d)\;0.66 atm$