$A$ solution is prepared by dissolving a $2.5 \ g$ sample of an unknown compound in $34 \ g$ of benzene,$C_6H_6$. The solution boils at $1.38 \ ^\circ C$ higher than pure benzene. Which expression gives the molar mass of the unknown compound? $K_b$ of $C_6H_6$ is $2.53 \ ^\circ C \ m^{-1}$.

• A
  $2.53 \times \frac{2.50}{1.38}$
• B
  $1.38 \times \frac{34}{2.53} \times 2.50$
• C
  $2.5 \times 10^3 \times \frac{2.53}{34} \times \frac{1}{1.38}$
• D
  $2.50 \times 10^3 \times \frac{1.38}{34} \times 2.53$