Q20 / 150 · MHT CET 2025 (21 Apr Shift 2) · Chemistry

Arrange the following solutions according to decreasing order of osmotic pressure under similar condition of temperature and assuming complete dissociation A. $0.2 \mathrm{~m~} \mathrm{KCl}$ B. $0.3 \mathrm{~m~} \mathrm{MgSO}_4$ C. $0 \cdot 1 \mathrm{~m~} \mathrm{BaCl}_2$ D. $0.5 \mathrm{~m~} \mathrm{Al}_2\left(\mathrm{SO}_4\right)_3$

  • Correct answer
    A
    $D>B>A>C$
  • B
    $\mathrm{C}>\mathrm{D}>\mathrm{A}>\mathrm{B}$
  • C
    $\mathrm{A}>\mathrm{C}>\mathrm{D}>\mathrm{B}$
  • D
    $\mathrm{B}>\mathrm{C}>\mathrm{A}>\mathrm{D}$

Solution

Osmotic pressure $\Pi = iCRT$, where $R$ and $T$ are constant. Therefore, the osmotic pressure is proportional to the product $iC$. Assuming complete dissociation, we calculate this product for each solution.

For $0.2\mathrm{ m} \mathrm{KCl}$, $i = 2$ and $C = 0.2$, so $iC = 2 \times 0.2 = 0.4$.

For $0.3\mathrm{ m} \mathrm{MgSO}_4$, $i = 2$ and $C = 0.3$, so $iC = 2 \times 0.3 = 0.6$.

For $0.1\mathrm{ m} \mathrm{BaCl}_2$, $i = 3$ and $C = 0.1$, so $iC = 3 \times 0.1 = 0.3$.

For $0.5\mathrm{ m} \mathrm{Al}_2(\mathrm{SO}_4)_3$, $i = 5$ and $C = 0.5$, so $iC = 5 \times 0.5 = 2.5$.

The $iC$ values are $2.5$, $0.6$, $0.4$, and $0.3$. The decreasing order is therefore $\mathrm{D} > \mathrm{B} > \mathrm{A} > \mathrm{C}$.

Conclusion: The correct option is $\boxed{\text{A}}$.

Hence, the correct answer is option: 'A'.

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