Question

Which of the following aqueous solutions exhibits lowest freezing point depression assuming complete dissociation?

• A. 0.1 m NaCl
• B. \(0.05\text{ }\mathrm{mMgSO}_{4}\)
• C. \(0.08\text{ }\mathrm{mAlPO}_{4}\)
• D. \(0.06\text{ }\mathrm{mAl}_{2}(\mathrm{SO}_{4})_{3}\)

Hint:

Freezing point depression is proportional to the effective number of particles, i times molality.

Answer 1

The Correct Option is B

Step 1: Understanding the Concept
\(\Delta T_f=i\,K_f\,m\), so the smallest \(i\times m\) gives the lowest depression.

Step 2: NaCl and MgSO4
\(0.1\times2=0.20\) for NaCl and \(0.05\times2=0.10\) for \(\text{MgSO}_4\).

Step 3: AlPO4 and Al2(SO4)3
\(0.08\times2=0.16\) for \(\text{AlPO}_4\) and \(0.06\times5=0.30\) for \(\text{Al}_2(\text{SO}_4)_3\).

Step 4: Result
The smallest value is 0.10, for 0.05 m \(\text{MgSO}_4\).

Final Answer:
0.05 m \(\text{MgSO}_4\) shows the lowest freezing point depression. \[ \boxed{\text{(B) }0.05\text{ m MgSO}_{4}} \]