Liquid Solution

2 g of naphthoic acid (molecular weight $=172 \mathrm{~g} \mathrm{~mol}^{-} 1$ ) dissolved in 20 mL of benzene shows a freezing point depression of 2 K . For benzene, the freezing point depression constant, $K_f=5$ $\mathrm{K} \mathrm{kg} \mathrm{mol}{ }^{-1}$ and the density is $0.88 \mathrm{~g} \mathrm{~mL}^{-1}$. What is the magnitude of the van't Hoff factor?