Which of the aqueous equimolal solution will have its vapour pressure near to solvent ?

Options

A. Urea
B. `Ba(NO_3)_2`
C. `NaNO_3`
D. `Al(NO_3)_3`

Explanation

To determine which of the aqueous equimolar solutions will have its vapor pressure nearest to that of the pure solvent, we need to analyze the effect of solute dissociation or association on vapor pressure.

### Step-by-Step Solution:

1. **Understanding Vapor Pressure**:
The vapor pressure of a solution is affected by the number of solute particles in the solution. The more particles present, the lower the vapor pressure compared to the pure solvent.

2. **Using Raoult's Law**:
According to Raoult's Law, the lowering of vapor pressure (ΔP) is given by:
\[ \Delta P = P_0 - P = P_0 \cdot X_2 \cdot i \]
where:
- \( P_0 \) = vapor pressure of the pure solvent
- \( P \) = vapor pressure of the solution
- \( X_2 \) = mole fraction of the solute
- \( i \) = van't Hoff factor (the number of particles the solute dissociates into)

3. **Identifying the Van't Hoff Factor (i)**:
- For Urea (NH2CONH2): Urea does not dissociate or associate, so \( i = 1 \).
- For Barium Nitrate (Ba(NO3)2): Dissociates into 1 Ba²⁺ and 2 NO3⁻, so \( i = 3 \).
- For Sodium Nitrate (NaNO3): Dissociates into 1 Na⁺ and 1 NO3⁻, so \( i = 2 \).
- For Aluminum Nitrate (Al(NO3)3): Dissociates into 1 Al³⁺ and 3 NO3⁻, so \( i = 4 \).

4. **Comparing the Values of i**:
- Urea: \( i = 1 \)
- Barium Nitrate: \( i = 3 \)
- Sodium Nitrate: \( i = 2 \)
- Aluminum Nitrate: \( i = 4 \)

5. **Determining Vapor Pressure Lowering**:
The lowering of vapor pressure is directly proportional to the product of the mole fraction of the solute and the van't Hoff factor. The lower the value of \( i \), the less the vapor pressure is lowered.

6. **Conclusion**:
Since Urea has the lowest van't Hoff factor (i = 1), it will cause the least lowering of vapor pressure. Therefore, the vapor pressure of the urea solution will be nearest to that of the pure solvent.

### Final Answer:
The aqueous equimolar solution that will have its vapor pressure nearest to that of the solvent is **Urea**.

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