Correct option (A) the pressure decreases
(B) the kinetic energy of the molecules remain the same
Explanation :
PV = nRT
(A) If gas is allowed to expand at constant temperature, P decreases (due to increase in V), hence true.
(B) K.E. = (3/2)nRT
KE ∝ temperature T hence (B) is also true.
(A) and (B) correct.