Which of the following aqueous solution should have the highest boiling point ?

Options

A. 1.0 M NaOH
B. 1.0 M `Na_2SO_4`
C. 1.0 M `NH_4NO_3`
D. 1.0 M `KNO_3`

Explanation

To determine which of the following aqueous solutions has the highest boiling point, we need to consider the van't Hoff factor (i) for each solute. The van't Hoff factor indicates the number of particles the solute dissociates into when dissolved in solution. The greater the number of particles, the higher the boiling point elevation.

### Step-by-Step Solution:

1. **Identify the compounds and their dissociation:**
- **NaOH:** Dissociates into Na⁺ and OH⁻.
- **Na₂SO₄:** Dissociates into 2 Na⁺ and SO₄²⁻.
- **NH₄NO₃:** Dissociates into NH₄⁺ and NO₃⁻.
- **KNO₃:** Dissociates into K⁺ and NO₃⁻.

2. **Calculate the van't Hoff factor (i) for each compound:**
- For **NaOH:**
- Dissociation: NaOH → Na⁺ + OH⁻
- i = 2 (1 Na⁺ + 1 OH⁻)
- For **Na₂SO₄:**
- Dissociation: Na₂SO₄ → 2 Na⁺ + SO₄²⁻
- i = 3 (2 Na⁺ + 1 SO₄²⁻)
- For **NH₄NO₃:**
- Dissociation: NH₄NO₃ → NH₄⁺ + NO₃⁻
- i = 2 (1 NH₄⁺ + 1 NO₃⁻)
- For **KNO₃:**
- Dissociation: KNO₃ → K⁺ + NO₃⁻
- i = 2 (1 K⁺ + 1 NO₃⁻)

3. **Compare the van't Hoff factors:**
- NaOH: i = 2
- Na₂SO₄: i = 3
- NH₄NO₃: i = 2
- KNO₃: i = 2

4. **Determine which solution has the highest boiling point:**
- Since the boiling point elevation is directly proportional to the van't Hoff factor, the solution with the highest i will have the highest boiling point.
- The highest van't Hoff factor is for **Na₂SO₄** (i = 3).

5. **Conclusion:**
- Therefore, the aqueous solution that should have the highest boiling point is **Na₂SO₄**.

### Final Answer:
**Na₂SO₄** has the highest boiling point among the given options.

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