We have a `0.1M` solution of `NH_(2)CONH_(2),H_(3)PO_(3)` and `H_(3)PO_(4)` then which of the following statement is correct, if we consider `100%` dissociation for `H_(3)PO_(3)` and `H_(3)PO_(4)`

Options

A. The V.P. and freezing pooint are highest for urea
B. The elevation in boiling point is the lowest for `H_(3)PO_(4)`
C. The V.P. and freezing point are the lowest for urea.
D. The depression in freezing point is the highest for `H_(3)PO_(3)`.

Answer

To solve the problem, we need to analyze the dissociation of the compounds in the solution and determine the number of particles produced from each compound. This will help us understand the colligative properties, which depend on the number of solute particles in the solution.

### Step-by-Step Solution:

1. **Identify the Compounds and Their Dissociation**:
- We have three compounds:
- Urea (NH₂CONH₂)
- Phosphorous acid (H₃PO₃)
- Phosphoric acid (H₃PO₄)

2. **Determine the Dissociation of Each Compound**:
- **Urea (NH₂CONH₂)**: Urea does not dissociate in solution. Therefore, it contributes **1 particle**.
- **Phosphorous acid (H₃PO₃)**: It dissociates completely into:
\[ H₃PO₃ \rightarrow 3H^+ + PO₃^{2-} \]
This results in **3 particles** (3 H⁺ ions and 1 PO₃²⁻ ion).
- **Phosphoric acid (H₃PO₄)**: It dissociates completely into:
\[ H₃PO₄ \rightarrow 3H^+ + PO₄^{3-} \]
This results in **4 particles** (3 H⁺ ions and 1 PO₄³⁻ ion).

3. **Count the Total Number of Particles**:
- For a **0.1 M solution**:
- Urea contributes: \(0.1 \, \text{M} \times 1 = 0.1 \, \text{mol}\)
- H₃PO₃ contributes: \(0.1 \, \text{M} \times 3 = 0.3 \, \text{mol}\)
- H₃PO₄ contributes: \(0.1 \, \text{M} \times 4 = 0.4 \, \text{mol}\)

4. **Analyze the Colligative Properties**:
- Colligative properties depend on the total number of solute particles in the solution.
- The more particles present, the greater the effect on properties such as vapor pressure lowering, freezing point depression, boiling point elevation, and osmotic pressure.

5. **Conclusion**:
- The total number of particles for each compound is:
- Urea: 1 particle
- H₃PO₃: 3 particles
- H₃PO₄: 4 particles
- Therefore, the compound with the highest effect on colligative properties is H₃PO₄, followed by H₃PO₃, and then urea.

### Correct Statement:
Based on the analysis, the correct statement is that the colligative properties will be maximum for H₃PO₄, followed by H₃PO₃, and the least for urea.