Which of the following solutions will exhibit the highest boiling poi…

The correct answer is Option (1) → 0.01 M Na₂SO₄ (aq)

Elevation of boiling point is a colligative property: \( \Delta T_b = i\,K_b\,m \). For dilute aqueous solutions the molality is close to the molarity, so the solution with the largest i × concentration (the most solute particles) boils highest.

• \( \ce{Na2SO4} \) — \( \ce{Na2SO4 -> 2Na^+ + SO4^2-} \), i = 3; 3 × 0.01 = 0.03.

• \( \ce{KNO3} \) — \( \ce{KNO3 -> K^+ + NO3^-} \), i = 2; 2 × 0.01 = 0.02.

• Urea — a non-electrolyte, i = 1; 1 × 0.015 = 0.015.

• Glucose — a non-electrolyte, i = 1; 1 × 0.015 = 0.015.

\( \ce{Na2SO4} \) gives the most particles, so its solution has the highest boiling point.

NCERT (2026-27 edition):
1.6.2 Elevation of Boiling Point – “… Similar to lowering of vapour pressure, the elevation of boiling point also depends on the number of solute molecules rather than their nature.”

1.7 Abnormal Molar Masses – “… In case of association, value of i is less than unity while for dissociation it is greater than unity.”