Step 1: Use freezing point depression relation.
Freezing point depression is given by:
\[
\Delta T_f=iK_fm
\]
where:
\[
i=\text{van't Hoff factor}
\]
\[
m=\text{molality}
\]
Higher the value of:
\[
i\times m
\]
greater is the depression in freezing point.
Hence, the solution with the smallest:
\[
i\times m
\]
will have the highest freezing point.
Step 2: Calculate \(i\times m\) for each solution.
For \(KCl\):
\[
KCl\rightarrow K^+ + Cl^-
\]
\[
i=2
\]
Thus,
\[
i\times m=2\times0.1=0.2
\]
For \(K_2SO_4\):
\[
K_2SO_4\rightarrow 2K^+ + SO_4^{2-}
\]
\[
i=3
\]
Thus,
\[
i\times m=3\times0.1=0.3
\]
For urea:
Urea is a non-electrolyte:
\[
i=1
\]
Thus,
\[
i\times m=1\times0.1=0.1
\]
For glucose:
Molar mass of glucose:
\[
180\ g\ mol^{-1}
\]
Moles of glucose:
\[
\frac{30}{180}=0.167\ mol
\]
Thus,
\[
m=0.167
\]
Since glucose is non-electrolyte:
\[
i=1
\]
Therefore,
\[
i\times m=0.167
\]
Step 3: Compare the values.
\[
K_2SO_4 : 0.3
\]
\[
KCl : 0.2
\]
\[
\text{Glucose} : 0.167
\]
\[
\text{Urea} : 0.1
\]
Smallest value is for urea.
Hence, urea solution has minimum freezing point depression and therefore highest freezing point.
Step 4: Final conclusion.
Therefore, the solution with highest freezing point is
\[
\boxed{0.1\ mol\ \text{Urea in}\ 1\ kg\ \text{water}}
\]