What is the correct sequence of the increasing order of freezing point at one atmosphere of the following 0.01 M aqueous solution?
1. Urea, 2. Potassium chloride, 3. potassium sulphate, 4. Potassium phosphate.
Select the correct answer using the codes gives below

Options

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

Answer

To determine the correct sequence of the increasing order of freezing point for the given 0.01 M aqueous solutions of urea, potassium chloride, potassium sulphate, and potassium phosphate, we need to analyze the dissociation of each solute in water and how it affects the freezing point.

### Step-by-Step Solution:

1. **Understanding Freezing Point Depression**:
The freezing point depression (ΔTf) is a colligative property, which means it depends on the number of solute particles in solution rather than the identity of the solute. The formula is:
\[ \Delta Tf = i \cdot K_f \cdot m \]
where:
- \( i \) = van 't Hoff factor (number of particles the solute dissociates into)
- \( K_f \) = freezing point depression constant (depends on the solvent)
- \( m \) = molality of the solution

2. **Determine the van 't Hoff factor (i) for each solute**:
- **Urea (NH₂CONH₂)**: Urea does not dissociate in solution, so \( i = 1 \).
- **Potassium Chloride (KCl)**: KCl dissociates into K⁺ and Cl⁻, so \( i = 2 \).
- **Potassium Sulphate (K₂SO₄)**: K₂SO₄ dissociates into 2 K⁺ and SO₄²⁻, so \( i = 3 \).
- **Potassium Phosphate (K₃PO₄)**: K₃PO₄ dissociates into 3 K⁺ and PO₄³⁻, so \( i = 4 \).

3. **Calculate the effective particle concentration**:
Since all solutions are 0.01 M, we can use the \( i \) values to determine the effective concentration of particles:
- Urea: \( 0.01 \cdot 1 = 0.01 \)
- KCl: \( 0.01 \cdot 2 = 0.02 \)
- K₂SO₄: \( 0.01 \cdot 3 = 0.03 \)
- K₃PO₄: \( 0.01 \cdot 4 = 0.04 \)

4. **Rank the solutions based on the effective particle concentration**:
The more particles in solution, the greater the freezing point depression, and thus the lower the freezing point:
- K₃PO₄ (0.04) < K₂SO₄ (0.03) < KCl (0.02) < Urea (0.01)

5. **Order the freezing points**:
Since we are looking for the increasing order of freezing points:
- Potassium Phosphate (lowest freezing point)
- Potassium Sulphate
- Potassium Chloride
- Urea (highest freezing point)

Thus, the correct sequence of increasing order of freezing point is:
\[ \text{Potassium Phosphate} < \text{Potassium Sulphate} < \text{Potassium Chloride} < \text{Urea} \]

### Final Answer:
The correct answer is: **4 < 3 < 2 < 1** (Potassium Phosphate < Potassium Sulphate < Potassium Chloride < Urea).