Question

Solutions A, B, C and D are respectively 0.2 M urea, 0.10 M NaCl, 0.05 M BaCl₂ and 0.05 M AlCl₃. All solutions are isotonic with each other except

• A. B
• B. A
• C. D
• D. C

Hint:

When comparing isotonic solutions, consider the dissociation of salts and their resulting ion concentration. More ions mean higher osmotic pressure.

Answer 1

The Correct Option is C

Step 1: Understanding isotonic solutions.
Isotonic solutions have the same osmotic pressure. The osmotic pressure is affected by the number of particles in solution. Thus, the solution with the highest number of ions per mole will deviate from being isotonic.

Step 2: Analyzing the options.
(A) B: This solution contains 2 ions per formula unit (NaCl).
(B) A: Urea does not dissociate, so it contributes 1 particle per molecule.
(C) D: AlCl₃ dissociates into 4 ions per formula unit, making it the most concentrated in terms of particles. Therefore, it is not isotonic.
(D) C: BaCl₂ dissociates into 3 ions per formula unit.

Step 3: Conclusion.
The correct answer is (C) D, as AlCl₃ gives the most ions, affecting the osmotic pressure.