Answer
D. 0.04 m (NH4)3PO4
Explanation
Boiling point elevation depends on the solvent, of course, but we're assuming water, and upon the concentration of the solute and how many particles into which the solute breaks. Colligative properties like boiling point elevation, depend on the total number of particles in solution. The solvent used here is water. So elevation in boiling point will be above a boiling point of water for all solutions.
ΔT= i x Kb x m,
Where i = van Hoff's factor, Kb = boiling point elevation constant of water = 0.512, m = molality
Higher ΔT will have a higher boiling point.
For 0.1 m CH4N₂O,
i = 1
ΔT = 1 x 0.512 x 0.1 = 0.0512
For 0.06 m HCI;
i = 2
ΔT = 2 x 0.512 x 0.06 = 0.06144
For 0.05 m CaCl2
i = 3
ΔT = 3 x 0.512 x 0.05 = 0.0768
For 0.04 m (NH4)3PO4;
i = 4
ΔT = 4 x 0.512 x 0.04 = 0.08192
For 0.07 m NaCl
i = 2
ΔT = 2 x 0.512 x 0.07 = 0.07168
0.04 m (NH4)3PO4 has the highest ΔT.
Therefore, the solution that has the highest boiling point would be D. 0.04 m (NH4)3PO4.
