 Density versus molar second virial convention

In the number-density virial expansion, $p/(n{k}_{B}T)=1+B_{2}n+\cdots$, so $B_2$ has units of volume. With molar concentration instead, the coefficient is $B_{2,\mathrm{mol}}=N_A{B}_2$, where $N_A$ is the Avogadro constant.