JEE Chemistry 2026 Question with Solution

Given: Four aqueous solutions of glucose, calcium chloride, urea and aluminium sulphate are given.

Find: The increasing order of boiling point.

Concept: Elevation in boiling point is a colligative property and depends on effective molality:

$$\Delta T_b = i K_b m$$

where $i$ is the van't Hoff factor and $m$ is the molality.

So, compare $i m$ for all four solutions.

I. Glucose is a non-electrolyte, so $i = 1$.

$$\text{Molar mass} = 180 \, \text{g mol}^{-1}$$ $$\text{Moles} = \frac{2.2}{180} \approx 0.0122$$ $$\text{Molality} = \frac{0.0122}{0.125} \approx 0.0976$$

Hence, effective molality $= 0.0976$.

II. Calcium chloride, $\mathrm{CaCl_2}$ dissociates into $\mathrm{Ca^{2+}}$ and $2\mathrm{Cl^-}$, so $i = 3$.

$$\text{Molar mass} = 111 \, \text{g mol}^{-1}$$ $$\text{Moles} = \frac{1.9}{111} \approx 0.0171$$ $$\text{Molality} = \frac{0.0171}{0.25} \approx 0.0684$$ $$\text{Effective molality} = 3 \times 0.0684 \approx 0.205$$

III. Urea is a non-electrolyte, so $i = 1$.

$$\text{Molar mass} = 60 \, \text{g mol}^{-1}$$ $$\text{Moles} = \frac{9}{60} = 0.15$$ $$\text{Molality} = \frac{0.15}{0.5} = 0.30$$

Hence, effective molality $= 0.30$.

IV. Aluminium sulphate, $\mathrm{Al_2(SO_4)_3}$ dissociates into $2\mathrm{Al^{3+}}$ and $3\mathrm{SO_4^{2-}}$, so $i = 5$.

$$\text{Molar mass} = 342 \, \text{g mol}^{-1}$$ $$\text{Moles} = \frac{20.5}{342} \approx 0.0599$$ $$\text{Molality} = \frac{0.0599}{0.75} \approx 0.0799$$ $$\text{Effective molality} = 5 \times 0.0799 \approx 0.399$$

Now compare the effective molalities:

$$\text{I} = 0.0976, \quad \text{II} = 0.205, \quad \text{III} = 0.30, \quad \text{IV} = 0.399$$

Since boiling point increases with increasing $\Delta T_b$, the increasing order of boiling point is:

$$\text{I} < \text{II} < \text{III} < \text{IV}$$

Therefore, the correct option is C.

The solution marks option B, but its own working and final order clearly give I < II < III < IV, which matches option C.