A freely moving piston divides a vertical cylinder, closed at both ends, into two parts each containing 1 mole of air. In equilibrium, at T=300 K, volume of the upper part is v=4 times greater than the lower part. At what temperature will the ratio of these volumes be equal to v′=2 ?
(a) 750 K
(b) 850 K
(c) 950 K
(d) 650 K