Arrange the given aqueous solutions in increasing order of their boil…

The correct answer is Option (2) → (A), (D), (C), (B)

Elevation of boiling point is a colligative property: it depends on the number of solute particles, not on their nature. For an electrolyte, the van’t Hoff factor (i) counts the particles produced by one formula unit:

    \( \displaystyle \Delta T_b=i\,K_b\,m \)

All four solutions have the same molality (0.1 m) and the same solvent (water, same K_b), so the boiling point rises with i alone. Assuming complete dissociation:

• (A) \( \ce{NH2CONH2} \) (urea): non-electrolyte, i = 1, i × m = 0.1

• (D) KCl → \( \ce{K^{+}} \) + \( \ce{Cl^{-}} \): i = 2, i × m = 0.2

• (C) \( \ce{Na2SO4} \) → \( \ce{2Na^{+}} \) + \( \ce{SO4^{2-}} \): i = 3, i × m = 0.3

• (B) \( \ce{AlCl3} \) → \( \ce{Al^{3+}} \) + \( \ce{3Cl^{-}} \): i = 4, i × m = 0.4

Shortcut: Urea (A) gives the fewest particles and \( \ce{AlCl3} \) (B) the most. Options (1) and (2) both start with (A) and end with (B); since KCl gives 2 ions and \( \ce{Na2SO4} \) gives 3, only Option (2) remains.