When common salt is dissolved in water

Options

A. The melting point of the solution increases.
B. The boiling point of the solution decreases.
C. Both melting point and boiling point decrease.
D. The boiling point of the solution increases.

Explanation

**Step-by-Step Solution:**

1. **Understanding the Dissolution of Common Salt (NaCl):**
- When common salt (sodium chloride, NaCl) is added to water, it dissolves. This process involves the separation of Na+ and Cl- ions.

2. **Dissociation of NaCl:**
- Sodium chloride is an ionic compound that dissociates into its constituent ions when it dissolves in water:
\[ \text{NaCl (s)} \rightarrow \text{Na}^+ (aq) + \text{Cl}^- (aq) \]

3. **Effect on Colligative Properties:**
- The presence of these ions affects the colligative properties of the solution, which depend on the number of solute particles in a solution rather than their identity.

4. **Van 't Hoff Factor (i):**
- The Van 't Hoff factor (i) for NaCl is 2 because it dissociates into two ions (Na+ and Cl-).
- For a non-electrolyte solute, the Van 't Hoff factor (i) is 1.

5. **Boiling Point Elevation (ΔTb):**
- The boiling point elevation can be calculated using the formula:
\[ \Delta T_b = i \cdot K_b \cdot m \]
- Here, \( K_b \) is the ebullioscopic constant of the solvent (water), and \( m \) is the molality of the solution.
- Since \( i \) increases (from 1 for a non-electrolyte to 2 for NaCl), the boiling point of the solution will increase.

6. **Freezing Point Depression (ΔTf):**
- The freezing point depression can be calculated using the formula:
\[ \Delta T_f = i \cdot K_f \cdot m \]
- Here, \( K_f \) is the cryoscopic constant of the solvent (water).
- As \( i \) increases, \( \Delta T_f \) also increases, which means the freezing point of the solution will decrease.

7. **Conclusion:**
- Thus, when common salt is dissolved in water, the boiling point of the solution increases, and the freezing point of the solution decreases.

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