Which of the following statements is/are correct?

AAccording to the third law, the entropy of a perfectly crystalline pure substance is zero at $0 K$ .
BAt $298 K$ the standard molar entropy order is $S^{\circ} (H X_{2} O (g)) > S^{\circ} (H X_{2} O (l))$ .
CIn an adiabatic irreversible process the entropy of the system increases.
DIn any spontaneous process $Δ S_{sys t e m}$ must be positive.

Answer: A, B, C

(A) The third law statement: true. (B) The gas phase has far more accessible microstates than the liquid: true. (C) With

q = 0

the irreversible process generates entropy,

Δ S_{sys} > 0

: true. (D) Only

Δ S_{t o t a l}

must be positive; a system's entropy can fall (e.g. freezing of water below

0^{\circ}

C) if the surroundings gain more: false.