Match the virial coefficient with its sign for a van der Waals gas. (P) $B$ at $T$ less than $T_{B}$ ; (Q) $B$ at $T$ greater than $T_{B}$ ; (R) $C = b^{2}$ at any $T$ . (1) positive; (2) negative. The correct matching is

Answer: A

B = b - a / RT

is negative below

T_{B}

and positive above it.

C = b^{2}

is a square and is always positive. So P-2, Q-1, R-1.