Which of the following aqueous solutions should have the highest boiling point?

Colligative property is an extensive property which depend on the number of moles of solute particles.
\(\begin{array}{|l|c|} \hline \text{ Aqueous Solution } & \text{ Number of Particles } \\ \hline \mathrm{NaOH} \rightarrow \mathrm{Na}^{+}+\mathrm{OH}^{-} & 2 \\ \hline \mathrm{Na}_{2} \mathrm{SO}_{4} \rightarrow 2 \mathrm{Na}^{+}+\mathrm{SO}_{4}^{2-} & 3 \\ \hline \mathrm{NH}_{4} \mathrm{NO}_{3} \rightarrow \mathrm{NH}_{4}^{+}+\mathrm{NO}_{3}^{-} & 2 \\ \hline \mathrm{KNO}_{3} \rightarrow \mathrm{K}^{+}+\mathrm{NO}_{3}^{-} & 2 \\ \hline \end{array}\)
Since, the concentration of the all compounds are same, therefore, compound having maximum no. of ions, that is,
\(\mathrm{Na}_{2} \mathrm{SO}_{4}\) will have highest boiling point.