# Which of the following solution boils at the highest temperature?

$\begin{array}{1 1}(a)\;0.1M\;sugar\\(b)\;0.1M\;MgCl_2\\(c)\;0.1M\;urea\\(d)\;0.1M\;AlCl_3\end{array}$

Answer: AlCl$_3$
The temperature at which vapour pressure of a liquid becomes equal to the external pressure present at the surface of the liquid is called boiling point of liquid at that pressure.
$\Delta Tb = i \times K_b \times m$ (molality)
In the given problem, $K_b$ and Molality are the same across solutions, so $\Delta T_b \propto i$.
Among the given choices $i_{AlCl_3} = 3, i_{MgCl_2} = 2, i_{\text{sugar}} = 1, i_{\text {urea}} = 1 \rightarrow AlCl_3$ will boil at the highest temperature.
edited Jul 16, 2014