What is the correct sequence of the increasing order of freezing points at one atmosphere of the following 1.0 M aqueous solution?
1. Urea, 2. Sodium chloride, 3. Sodium sulphate, 4. Sodium phosphate.
Select the correct answer using the codes given below

Options

A. 4, 3, 1, 2
B. 3, 4, 2, 1
C. 3 4, 1, 2
D. 4, 3, 2, 1

Answer

To determine the correct sequence of the increasing order of freezing points for the given 1.0 M aqueous solutions of Urea, Sodium Chloride, Sodium Sulfate, and Sodium Phosphate, we will use the concept of colligative properties, specifically the depression of freezing point (ΔTf).

### Step-by-Step Solution:

1. **Understanding Freezing Point Depression**:
The freezing point depression is given by the formula:
\[ \Delta T_f = i \cdot K_f \cdot m \]
where:
- \( \Delta T_f \) is the depression in freezing point,
- \( i \) is the van 't Hoff factor (the number of particles the solute dissociates into),
- \( K_f \) is the freezing point depression constant of the solvent (water in this case),
- \( m \) is the molality of the solution.

2. **Identifying the van 't Hoff Factor (i)**:
- **Urea (NH2CO-NH2)**: Urea does not dissociate in solution, so \( i = 1 \).
- **Sodium Chloride (NaCl)**: Dissociates into 2 ions (Na\(^+\) and Cl\(^-\)), so \( i = 2 \).
- **Sodium Sulfate (Na2SO4)**: Dissociates into 3 ions (2 Na\(^+\) and SO4\(^{2-}\)), so \( i = 3 \).
- **Sodium Phosphate (Na3PO4)**: Dissociates into 4 ions (3 Na\(^+\) and PO4\(^{3-}\)), so \( i = 4 \).

3. **Calculating the Depression in Freezing Point**:
Since the concentration (1.0 M) and \( K_f \) are the same for all solutions, the depression in freezing point will depend solely on the value of \( i \):
- For Urea: \( \Delta T_f = 1 \cdot K_f \cdot 1.0 \)
- For NaCl: \( \Delta T_f = 2 \cdot K_f \cdot 1.0 \)
- For Na2SO4: \( \Delta T_f = 3 \cdot K_f \cdot 1.0 \)
- For Na3PO4: \( \Delta T_f = 4 \cdot K_f \cdot 1.0 \)

4. **Determining the Order of Freezing Points**:
The greater the value of \( i \), the lower the freezing point (greater depression). Therefore, the order of depression in freezing point is:
- Urea (i = 1) > NaCl (i = 2) > Na2SO4 (i = 3) > Na3PO4 (i = 4)

5. **Increasing Order of Freezing Points**:
Since we need the increasing order of freezing points, we reverse the order of depression:
- Urea (highest freezing point) > NaCl > Na2SO4 > Na3PO4 (lowest freezing point)

Thus, the increasing order of freezing points is:
**Urea < Sodium Chloride < Sodium Sulfate < Sodium Phosphate**.

### Final Answer:
1. Urea
2. Sodium Chloride
3. Sodium Sulfate
4. Sodium Phosphate