Which of the following solutions have lowest freezing point ?

Options

A. 0.1 M NaCl
B. 0.01 M NaCl
C. 1M NaCl
D. 0.001 M NaCl

Answer

To determine which of the given solutions has the lowest freezing point, we can follow these steps:

### Step 1: Understand the Concept of Freezing Point Depression
The freezing point depression (ΔTf) is given by the formula:
\[ \Delta Tf = Kf \times m \]
where:
- \( Kf \) is the cryoscopic constant (a property of the solvent),
- \( m \) is the molality of the solution.

### Step 2: Relate Molality to Molarity
Molality (m) is defined as the number of moles of solute per kilogram of solvent. However, for dilute solutions, we can relate molality to molarity (M) since the density of the solution remains approximately constant. Thus, we can express molality in terms of molarity:
\[ m \propto M \]
This means that the freezing point depression is directly proportional to the molarity of the solution.

### Step 3: Compare the Molarities of the Given Solutions
To find which solution has the lowest freezing point, we need to compare the molarity of the given NaCl solutions. The solution with the highest molarity will have the lowest freezing point.

### Step 4: Identify the Solution with Highest Molarity
Assuming we have the following options:
1. 0.5 M NaCl
2. 1.0 M NaCl
3. 0.1 M NaCl
4. 0.75 M NaCl

From these options, we can see that:
- 1.0 M NaCl has the highest molarity.

### Step 5: Conclusion
Since the freezing point depression is directly proportional to molarity, the solution with the highest molarity (1.0 M NaCl) will have the lowest freezing point.

Thus, the answer is:
**1.0 M NaCl** has the lowest freezing point.

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